Add alert management functionality in backend and frontend

This commit introduces alert management capabilities, including creating, updating, listing, and removing custom SQL-based alerts in the backend. It adds the necessary database migrations, API endpoints, and frontend pages to manage alerts, enabling users to define thresholds and monitor system health effectively.

backend/app/api/router.py

@@ -1,9 +1,10 @@
 from fastapi import APIRouter
-from app.api.routes import admin_users, auth, health, me, targets
+from app.api.routes import admin_users, alerts, auth, health, me, targets
 
 api_router = APIRouter()
 api_router.include_router(health.router, tags=["health"])
 api_router.include_router(auth.router, prefix="/auth", tags=["auth"])
 api_router.include_router(me.router, tags=["auth"])
 api_router.include_router(targets.router, prefix="/targets", tags=["targets"])
+api_router.include_router(alerts.router, prefix="/alerts", tags=["alerts"])
 api_router.include_router(admin_users.router, prefix="/admin/users", tags=["admin"])