Add OpenAPI/Swagger documentation

- Add Swagger dependencies to go.mod
- Annotate all API endpoints with Swagger comments
- Add Swagger UI at /api/v1/docs endpoint
- Auto-generate Swagger docs in Dockerfile build
- Update README with API documentation link

README.md

@@ -79,7 +79,7 @@ go run cmd/api/main.go
 
 ## API Documentation
 
-Once running, visit `http://localhost:8080/api/v1/docs` for interactive API documentation.
+Once running, visit `http://localhost:8080/api/v1/docs` for interactive Swagger documentation.
 
 ## Architecture