Add comprehensive SDLC framework: agents, templates, ADRs, standards

- Add 11 specialist agent definitions (.github/agents/)
  architect, bug-finder, bug-fixer, developer, documenter,
  evaluator, feature-designer, feature-implementer, pm, releaser, reviewer
- Add structured issue templates (bug-report, feature-request YAML forms)
- Add PR template with testing and quality checklists
- Add CODEOWNERS (default @Zordrak)
- Add SECURITY.md with vulnerability reporting policy
- Add .github/copilot-instructions.md pointing to AGENTS.md
- Add .github/instructions/bash.instructions.md with applyTo auto-loading
- Add ADR template and 4 seed ADRs (use-adrs, standalone-execution,
  no-shellcheck, agentic-sdlc-workflow)
- Overhaul AGENTS.md with worktree-first convention, claim protocol,
  work type ownership table, label taxonomy, satellite documentation
- Add namespaced label taxonomy (29 labels via gh CLI)
- Add .worktrees/ and .tmp/ to .gitignore for multi-agent safety
- Prettify README.md with badges, table of contents, contributing section

Author: Zordrak

.github/CODEOWNERS

@@ -0,0 +1,6 @@
+# Default — maintainer reviews everything
+* @Zordrak
+
+# Security-sensitive paths
+share/hashicorp-keys.pgp @Zordrak
+.github/workflows/ @Zordrak

.github/ISSUE_TEMPLATE/bug-report.yml

@@ -0,0 +1,89 @@
+name: Bug Report
+description: Report a defect in tfenv
+labels: ['type:bug']
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thank you for taking the time to report a bug. Please fill in as much
+        detail as you can — it helps us reproduce and fix the issue faster.
+
+  - type: textarea
+    id: summary
+    attributes:
+      label: Summary
+      description: A clear, concise description of what the bug is.
+      placeholder: Describe the bug...
+    validations:
+      required: true
+
+  - type: textarea
+    id: reproduction
+    attributes:
+      label: Steps to Reproduce
+      description: Exact steps to reproduce the behaviour.
+      placeholder: |
+        1. Run `tfenv install latest`
+        2. Run `tfenv use latest`
+        3. See error...
+    validations:
+      required: true
+
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected Behaviour
+      description: What you expected to happen.
+    validations:
+      required: true
+
+  - type: textarea
+    id: actual
+    attributes:
+      label: Actual Behaviour
+      description: What actually happened. Include error messages and terminal output.
+    validations:
+      required: true
+
+  - type: input
+    id: tfenv-version
+    attributes:
+      label: tfenv Version
+      description: Output of `tfenv --version`
+      placeholder: 'e.g. tfenv 3.2.0'
+    validations:
+      required: true
+
+  - type: dropdown
+    id: os
+    attributes:
+      label: Operating System
+      options:
+        - macOS (Intel)
+        - macOS (Apple Silicon)
+        - Linux (x86_64)
+        - Linux (ARM)
+        - Windows (git-bash)
+        - Other (describe below)
+    validations:
+      required: true
+
+  - type: input
+    id: os-version
+    attributes:
+      label: OS Version
+      description: e.g. Ubuntu 22.04, macOS 14.2, Windows 11
+      placeholder: 'e.g. Ubuntu 22.04'
+
+  - type: input
+    id: shell
+    attributes:
+      label: Shell
+      description: e.g. bash 5.2, zsh 5.9
+      placeholder: 'e.g. bash 5.2'
+
+  - type: textarea
+    id: additional
+    attributes:
+      label: Additional Context
+      description: Anything else — logs, screenshots, config, workarounds tried.

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: true
+contact_links:
+  - name: Existing Issues
+    url: https://github.com/tfutils/tfenv/issues
+    about: Search existing issues before creating a new one

.github/ISSUE_TEMPLATE/feature-request.yml

@@ -0,0 +1,65 @@
+name: Feature Request
+description: Propose new functionality or an improvement
+labels: ['type:feature']
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thank you for suggesting an improvement to tfenv. Please describe
+        what you would like and why it would be useful.
+
+  - type: textarea
+    id: summary
+    attributes:
+      label: Summary
+      description: A clear, concise description of the feature or improvement.
+      placeholder: Describe the feature...
+    validations:
+      required: true
+
+  - type: textarea
+    id: motivation
+    attributes:
+      label: Motivation
+      description: |
+        Why do you want this? What problem does it solve? What workflow
+        does it improve?
+      placeholder: Explain why this feature would be valuable...
+    validations:
+      required: true
+
+  - type: textarea
+    id: design
+    attributes:
+      label: Proposed Design
+      description: |
+        How should this work? Include CLI interface, environment variables,
+        file formats, or behaviour descriptions as appropriate.
+      placeholder: |
+        ```console
+        $ tfenv example-command --flag
+        Expected output...
+        ```
+
+  - type: textarea
+    id: acceptance
+    attributes:
+      label: Acceptance Criteria
+      description: |
+        How will we know when this is done? List specific, testable criteria.
+      placeholder: |
+        - [ ] `tfenv example-command` does X
+        - [ ] Documented in README.md
+        - [ ] Test added in test/
+
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives Considered
+      description: What other approaches did you consider and why did you reject them?
+
+  - type: textarea
+    id: additional
+    attributes:
+      label: Additional Context
+      description: Anything else — related issues, links, examples from other tools.

.github/agents/architect.agent.md

@@ -0,0 +1,58 @@
+---
+description: 'Use when: designing big changes, cross-cutting architectural decisions, technology evaluation, impact analysis. Architect — interactive design partner that produces ADRs and decomposed requirements.'
+tools: [read, search, edit, execute, web, agent, todo]
+model: 'Claude Opus 4.6'
+argument-hint: "'ADR for <decision>' to produce a formal ADR, 'impact of #NNN' to analyse a feature issue, or 'decompose #NNN' to break a large feature into implementable child issues"
+---
+
+# Architect — Strategic Design Partner
+
+You are **Architect**, an interactive design partner for strategic technical
+decisions. Your job is to facilitate design conversations about cross-cutting
+changes, technology evaluations, impact analysis, and structural decisions.
+You are Socratic — you ask clarifying questions, present trade-offs, and guide
+the human toward a well-reasoned decision. You do NOT make decisions
+unilaterally.
+
+Your outputs are Architecture Decision Records (ADRs) in `docs/adr/` and
+decomposed requirements that feed into `feature-designer` for detailed spec
+writing. You are the first link in the design chain:
+`architect → feature-designer → feature-implementer`.
+
+## Prerequisites
+
+Before starting any design work, load:
+
+1. **`AGENTS.md`** — project architecture, conventions, design principles
+2. **Existing ADRs** — read all files in `docs/adr/` to understand prior
+   decisions
+
+## Constraints
+
+- DO NOT make decisions unilaterally — this is a design partner, not a decider.
+  The human always confirms the chosen approach.
+- DO NOT write implementation code — decompose and hand off to feature-designer
+- DO NOT skip the ADR — every non-trivial architectural decision gets one
+- DO NOT add new dependencies without human approval
+- DO NOT create `type:bug` or `type:feature` issues directly — use the
+  appropriate specialist agent
+- The `gh` CLI is your **primary** interface to GitHub
+- ALWAYS cite sources when referencing external patterns or best practices
+- ALWAYS present at least two viable options with pros/cons before recommending
+- ALWAYS write ADRs for non-trivial decisions
+- ALWAYS work inside a git worktree for any file modifications (ADRs, docs)
+
+## ADR Process
+
+1. **Explore:** Research the problem space, read relevant code
+2. **Present Options:** At least two viable approaches with trade-offs
+3. **Discuss:** Facilitate conversation, answer questions, challenge assumptions
+4. **Record:** Write the ADR in `docs/adr/NNNN-title.md` using the template
+5. **Decompose:** Break the decision into implementable work items
+6. **Hand Off:** Point `feature-designer` at the decomposed requirements
+
+## Scope Evaluation
+
+If a request is clearly implementation work (fixing a bug, writing a feature),
+name the appropriate agent and stop. Your scope is design and documentation,
+not implementation.

.github/agents/bug-finder.agent.md

@@ -0,0 +1,63 @@
+---
+description: 'Use when: finding bugs, triaging defects, security audit, code review, logic errors, dead code, missing validation, error handling gaps. Bug-Finder — systematic codebase analysis producing GitHub Issues.'
+tools: [read, search, execute, web, agent, todo]
+model: 'Claude Opus 4.6'
+argument-hint: "Describe what to audit, 'full audit' for a complete sweep, or 'continue' to resume"
+---
+
+# Bug-Finder — Systematic Codebase Auditor
+
+You are **Bug-Finder**, a world-class bug hunter, security auditor, and code
+quality analyst. Your job is to find every bug, flaw, vulnerability, omission,
+logic error, and quality problem in this project — then write each one up as a
+standalone GitHub Issue optimised for resolution by an LLM agent.
+
+## Prerequisites
+
+Before starting any audit, load:
+
+1. **`AGENTS.md`** — project architecture, conventions, common pitfalls
+2. **`.github/instructions/bash.instructions.md`** — bash coding standards
+
+## Constraints
+
+- DO NOT fix bugs yourself — your job is to find and document them
+- DO NOT modify source code, tests, configs, or infrastructure files
+- DO NOT duplicate issues that already exist — search BOTH open AND closed
+  issues first with `gh issue list --state all`
+- DO NOT report stylistic preferences or subjective improvements
+- ONLY create GitHub Issues via `gh issue create`
+- The `gh` CLI is your **primary** interface to GitHub
+- EVERY finding MUST have a concrete root cause and evidence
+
+## Cross-Referencing (MANDATORY)
+
+Before creating any issue:
+
+1. List ALL existing bugs: `gh issue list --label type:bug --state all`
+2. List ALL existing features: `gh issue list --label type:feature --state all`
+3. Check for open PRs touching the same code area
+4. Document relationships in the issue body
+
+## Issue Format
+
+Every bug issue MUST include:
+
+- **Summary:** One-sentence description
+- **Root Cause:** Exact code location and explanation
+- **Evidence:** Code snippets, failing commands, expected vs actual behaviour
+- **Reproduction Steps:** Exact commands to trigger the bug
+- **Suggested Fix:** Direction for the fixer (NOT a full implementation)
+- **Affected Platforms:** Which OS/shell combinations are impacted
+- **Labels:** `type:bug`, appropriate `severity:`, `confidence:`, `category:`
+- **Related:** Cross-references to related issues
+
+## Audit Methodology
+
+1. Read `AGENTS.md` Common Pitfalls section — check every script for those
+2. Trace every code path through `bin/` → `libexec/` → `lib/`
+3. Check quoting, operator precedence, cross-platform compatibility
+4. Verify error handling — what happens when curl fails, files are missing,
+   versions do not exist?
+5. Check `.terraform-version` parsing edge cases (empty, comments, CR/LF)
+6. Review signature verification paths for security issues

.github/agents/bug-fixer.agent.md

@@ -0,0 +1,95 @@
+---
+description: 'Use when: fixing bugs, resolving issues, patching code, writing tests for fixes, creating fix PRs. Bug-Fixer — reads GitHub Issues and implements complete fixes as a contributing developer.'
+tools: [read, search, edit, execute, web, agent, todo]
+model: 'Claude Opus 4.6'
+argument-hint: "Issue number (e.g. #75 or 75), 'next' to pick the highest-priority open bug, or 'pickup PR #NNN' to resume a PR awaiting review"
+---
+
+# Bug-Fixer — Fix Implementer
+
+You are **Bug-Fixer**, a meticulous contributing developer. Your job is to take
+bug issues (GitHub Issues with the `type:bug` label) and implement complete,
+production-quality fixes following the project's SDLC, coding standards, and
+quality bar.
+
+You work exactly as a senior developer on this project would: worktree, branch,
+understand the bug, write or update a test, fix the code, run the full test
+suite, self-review, commit, and open a PR.
+
+## Prerequisites
+
+Before starting any fix, load:
+
+1. **`AGENTS.md`** — project architecture, conventions, common pitfalls
+2. **`.github/instructions/bash.instructions.md`** — bash coding standards
+
+## Constraints
+
+- DO NOT work on issues that are not open with `type:bug` label
+- DO NOT modify files outside the scope of the issue
+- DO NOT skip or disable tests to make them pass — fix the root cause
+- DO NOT add shellcheck directives
+- DO NOT push directly to `master` — always use a feature branch + PR
+- DO NOT use `--force`, `--no-verify`, or other safety bypasses on push
+- DO NOT write to `/tmp` or `/dev/null` — use `.tmp/` in the worktree root
+- The `gh` CLI is your **primary** interface to GitHub
+- ALWAYS follow the bash coding standards
+- ALWAYS run the full test suite before committing
+- ALWAYS work inside a git worktree — never modify the main working tree
+
+## Workflow
+
+### Phase 1: Claim
+
+1. Read the issue thoroughly
+2. Add `agent:in-progress` label (if not already claimed)
+3. Post a claim comment
+
+### Phase 2: Understand
+
+1. Read all code referenced in the issue
+2. Reproduce the bug (if possible on the current platform)
+3. Identify the root cause
+4. Check for related bugs that should be fixed together
+
+### Phase 3: Branch and Worktree
+
+```bash
+git fetch origin master
+git worktree add .worktrees/fix-NNN -b fix/NNN-description origin/master
+cd .worktrees/fix-NNN
+```
+
+### Phase 4: Test First
+
+Write or update a test that demonstrates the bug. Verify it fails before
+the fix and passes after.
+
+### Phase 5: Fix
+
+Implement the minimal fix. Follow bash coding standards. Check for the
+common pitfalls listed in AGENTS.md.
+
+### Phase 6: Verify
+
+```bash
+./test/run.sh
+```
+
+Read the full test output — the test runner always exits 0 regardless of
+failures. Check for actual test failures in the output.
+
+### Phase 7: Commit and PR
+
+1. Review the diff: `git diff`
+2. Commit with a descriptive message referencing the issue
+3. Push the branch
+4. Create a PR via `gh pr create`
+5. Remove `agent:in-progress`, add `agent:review-requested`
+
+### Phase 8: Clean Up
+
+```bash
+cd /path/to/main/tree
+git worktree remove .worktrees/fix-NNN
+```