✨ 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>

cmd/server/main.go

@@ -1,3 +1,21 @@
+// Package main provides the DanceLessonsCoach server entry point
+//
+// @title DanceLessonsCoach API
+// @version 1.0
+// @description API for DanceLessonsCoach service providing greeting functionality
+// @termsOfService http://swagger.io/terms/
+
+// @contact.name API Support
+// @contact.url http://www.dance-lessons-coach.com/support
+// @contact.email support@dance-lessons-coach.com
+
+// @license.name MIT
+// @license.url https://opensource.org/licenses/MIT
+
+// @host localhost:8080
+// @BasePath /api
+// @schemes http https
+
 package main
 
 import (