chore: add Release Please workflow and ADR issue template

[Pawansingh3889]

What changed

Two things that compose with the existing release pipeline and issue templates without changing user-facing behaviour:

1. ADR issue template (.github/ISSUE_TEMPLATE/adr.yml) — captures the shape used by the W025 and dbt-aware rule pack ADRs (What / Why / Scope / Compatibility / Plan / Open questions / Rejected). Stops the next architecture proposal from being typed by hand into a blank textarea.
2. Release Please — release-please-config.json + .release-please-manifest.json (pinned at v0.7.0) + .github/workflows/release-please.yml. Watches main for Conventional Commits, opens a release PR with version bump + CHANGELOG promotion, and on merge cuts a v*.*.* tag. The existing release.yml already triggers on tags and publishes to PyPI via Trusted Publishing — no change there.

Related issue

None. Triggered by external review feedback on contributor-friction and release-chore overhead.

If this adds or changes a rule

N/A — no rule changes.

Tests

• pytest -q passes (254 passed / 1 skipped, unchanged from main)
• ruff check . passes

This PR only touches .github/ and root-level config — no test changes expected.

Checklist

• One logical change per commit; Conventional Commits style (chore, ci)
• No CHANGELOG.md entry — infra/governance only, not user-facing behaviour

Anything else reviewers should know

What the first Release Please PR will look like. After this merges, RP will sweep up every Conventional Commit since v0.7.0 — currently that's W024, the S001 fix, E009, T006, plus anything else that has landed. Two decisions on that release PR:

1. CHANGELOG content. RP auto-generates entries from commit subjects. The existing [Unreleased] section has hand-written prose with more context than commit subjects carry. Keep the prose (delete RP's terse entries) or accept RP's entries (delete the prose). I'd keep the prose.
2. Branch merge order. If feature/W025-assertion-malformed and feature/dbt-pack-scaffold land before this, they go into the first auto-cut release. If this lands first, the auto-cut release is chore-only (v0.7.1). Recommended order: W025 → DBT001 → this branch last.

Permissions. The workflow declares contents: write and pull-requests: write for release-please-action. No new secrets; uses GITHUB_TOKEN.

Reversibility. If RP misbehaves, deleting .github/workflows/release-please.yml cleanly disables it. The manifest + config can stay.