feat: Admin Operations SIEM — alerts, notifications, pre-built rules

- Add pluggable notification system (webhook, Slack, Teams) with retry
- Add alert deduplication: same rule + actor within 15 min = one alert
- Add 10 pre-built admin-ops rule templates seeded on startup:
  - Failed Conditional Access, After-Hours Admin Activity
  - New Application Registration, Admin Role Assignment
  - License Change, Bulk User Deletion
  - Device Compliance Failure, Exchange Transport Rule Change
  - Service Principal Credential Added, External Sharing Enabled
- Add /api/alerts, /api/alerts/{id}/status, /api/alerts/summary endpoints
- Add alert dashboard to frontend with status filters and ack/resolve buttons
- Add alert summary badge in hero header (high/medium/low counts)
- New env vars: ALERT_WEBHOOK_URL, ALERT_WEBHOOK_FORMAT, ALERT_DEDUPE_MINUTES

backend/main.py

@@ -14,6 +14,7 @@ from fastapi.responses import Response
 from fastapi.staticfiles import StaticFiles
 from metrics import observe_request, prometheus_metrics
 from middleware import CorrelationIdMiddleware
+from routes.alerts import router as alerts_router
 from routes.config import router as config_router
 from routes.events import router as events_router
 from routes.fetch import router as fetch_router
@@ -123,6 +124,7 @@ if AI_FEATURES_ENABLED:
     app.mount("/mcp", mcp_asgi)
 app.include_router(saved_searches_router, prefix="/api")
 app.include_router(rules_router, prefix="/api")
+app.include_router(alerts_router, prefix="/api")
 app.include_router(jobs_router, prefix="/api")
 
 
@@ -167,6 +169,9 @@ async def _periodic_fetch():
 @app.on_event("startup")
 async def start_periodic_fetch():
     setup_indexes()
+    from rules import seed_default_rules
+
+    seed_default_rules()
     if ENABLE_PERIODIC_FETCH:
         app.state.fetch_task = asyncio.create_task(_periodic_fetch())