feat(17-02): SNMP profile CRUD API and SNMP metrics query endpoint

- Add Pydantic schemas for SNMP profile CRUD (list excludes profile_data JSONB)
- Add 5-route SNMP profiles router with system profile protection (403)
- Add device deletion protection for referenced profiles (409)
- Add time-bucketed SNMP metrics query endpoint with metric_name/group filters
- Add distinct metric names endpoint for frontend dropdowns
- Register snmp_profiles_router in main.py

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/main.py

@@ -462,6 +462,7 @@ def create_app() -> FastAPI:
     from app.routers.settings import router as settings_router
     from app.routers.remote_access import router as remote_access_router
     from app.routers.winbox_remote import router as winbox_remote_router
+    from app.routers.snmp_profiles import router as snmp_profiles_router
     from app.routers.sites import router as sites_router
     from app.routers.links import router as links_router
     from app.routers.sectors import router as sectors_router
@@ -496,6 +497,7 @@ def create_app() -> FastAPI:
     app.include_router(settings_router, prefix="/api")
     app.include_router(remote_access_router, prefix="/api")
     app.include_router(winbox_remote_router, prefix="/api")
+    app.include_router(snmp_profiles_router, prefix="/api")
     app.include_router(sites_router, prefix="/api")
     app.include_router(links_router, prefix="/api")
     app.include_router(sectors_router, prefix="/api")