✨ feat: implement OpenAPI/Swagger documentation with swaggo/swag

📝 docs: add comprehensive API documentation
📦 dependencies: add swaggo/swag to go.mod
🔧 chore: add go:generate directive for documentation

- Add comprehensive API documentation using swaggo/swag
- Embed OpenAPI spec in binary using go:embed
- Add Swagger UI at /swagger/
- Document all endpoints, models, and validation rules
- Add go:generate directive for easy regeneration
- Update README, AGENTS, CHANGELOG with documentation
- Finalize ADR 0013 with implementation details
- Gitignore generated docs directory

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

CHANGELOG.md

@@ -114,6 +114,39 @@ echo "## Compact History (Last 5 Entries)" > CHANGELOG.md
 git log -5 --pretty=format:"### %ad%n- %s%n" -- CHANGELOG.md >> CHANGELOG.md
 ```
 
+## 2026-04-05 - OpenAPI Documentation Implementation
+
+### ✅ Completed
+- **OpenAPI/Swagger Integration**: Added comprehensive API documentation using swaggo/swag
+- **Embedded Documentation**: OpenAPI spec embedded in binary using `//go:embed` directive
+- **Interactive Swagger UI**: Available at `/swagger/` with try-it-out functionality
+- **Code Generation**: Added `//go:generate` directive for easy documentation regeneration
+- **Clean Structure**: Documentation in `pkg/server/docs/` (gitignored)
+
+### 📝 Changes
+- `cmd/server/main.go`: Added swagger metadata annotations
+- `pkg/greet/api_v1.go`: Documented v1 endpoints and models
+- `pkg/greet/api_v2.go`: Documented v2 endpoint
+- `pkg/server/server.go`: Added embed directive and swagger routes
+- `.gitignore`: Added `pkg/server/docs/`
+- `go.mod/go.sum`: Added swaggo dependencies
+
+### 🔧 Workflow
+```bash
+# Generate documentation
+go generate ./pkg/server/
+
+# Access documentation
+# Swagger UI: http://localhost:8080/swagger/
+# OpenAPI spec: http://localhost:8080/swagger/doc.json
+```
+
+### 📚 Documentation
+- All API endpoints documented with summaries, descriptions, parameters
+- Request/response models with examples
+- Validation rules and error responses
+- Tags for logical grouping
+
 ## References
 
 - **Agent Config**: `/Users/gabrielradureau/Work/Vibe/.mistral/dancelessonscoachprogrammer-agent.toml`