chore: add repository-specific copilot instructions (#21)

Author: beonde

.github/copilot-instructions.md

@@ -0,0 +1,68 @@
+# capiscio-docs - GitHub Copilot Instructions
+
+## ABSOLUTE RULES - NO EXCEPTIONS
+
+### 1. ALL WORK VIA PULL REQUESTS
+- **NEVER commit directly to `main`.** All changes MUST go through PRs.
+
+### 2. RFCs ARE READ-ONLY
+- **DO NOT modify RFCs** — they live in `capiscio-rfcs/`, not here.
+
+### 3. NO WATCH/BLOCKING COMMANDS
+- **NEVER run blocking commands** without timeout
+
+---
+
+## CRITICAL: Read First
+
+**Before starting work, read the workspace context files:**
+1. `../../.context/CURRENT_SPRINT.md` - Sprint goals and priorities
+2. `../../.context/ACTIVE_TASKS.md` - Active tasks
+
+---
+
+## Repository Purpose
+
+**capiscio-docs** is the unified public documentation site for CapiscIO, published via MkDocs at docs.capisc.io.
+
+It aggregates docs from multiple repos into a single site.
+
+**Technology Stack**: MkDocs (Material theme), Python, Markdown
+
+**Default Branch:** `main`
+
+## Structure
+
+```
+capiscio-docs/
+├── mkdocs.yml               # MkDocs configuration (nav, theme, plugins)
+├── requirements-docs.txt    # Python deps (mkdocs, material, plugins)
+├── docs/
+│   ├── index.md             # Landing page
+│   ├── getting-started/     # Quickstart, installation
+│   ├── how-to/              # Task-oriented guides (integrations, middleware)
+│   ├── reference/           # API reference (SDK, CLI, server)
+│   ├── concepts/            # Architecture, trust model, DID
+│   └── rfcs/                # RFC summaries (detail in capiscio-rfcs)
+├── scripts/                 # Build/sync scripts
+└── site/                    # Generated output (gitignored)
+```
+
+## Quick Commands
+
+```bash
+pip install -r requirements-docs.txt   # Install deps
+mkdocs serve                           # Dev server (localhost:8000)
+mkdocs build                           # Build static site
+make serve                             # Alias for mkdocs serve
+```
+
+## Documentation Standards
+
+- **Diataxis framework**: tutorials → how-to → reference → concepts
+- **Cross-repo accuracy**: Docs must match actual SDK/server/core APIs
+- Use `admonitions` for warnings/notes: `!!! warning`, `!!! note`
+- Code examples must be tested or derived from actual working code
+- When documenting SDK APIs, verify against `capiscio-sdk-python` source
+- When documenting server APIs, verify against `capiscio-server` swagger
+- Internal docs go in `internal-docs/` (workspace root), NOT here