- New app/api/metrics.py: GET /api/metrics, GET /api/metrics/{id:path},
POST /api/admin/metrics (201), DELETE /api/admin/metrics/{id:path}
- Add require_admin dependency to app/auth/dependencies.py
- Register metrics_router in app/main.py before web_router
- Deprecate GET /api/catalog/metrics/{path} with 301 redirect to new endpoint
- 7 new tests in TestMetricsAPI covering CRUD, 404, RBAC, category filter
