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/routes/alerts.py

@@ -0,0 +1,78 @@
+"""Alert management endpoints."""
+
+from auth import require_auth
+from bson import ObjectId
+from database import alerts_collection
+from fastapi import APIRouter, Depends, HTTPException, Query
+from pydantic import BaseModel
+
+router = APIRouter(dependencies=[Depends(require_auth)])
+
+
+class AlertStatusUpdate(BaseModel):
+    status: str  # open | acknowledged | resolved | false_positive
+
+
+class AlertListResponse(BaseModel):
+    items: list[dict]
+    total: int
+
+
+@router.get("/alerts", response_model=AlertListResponse)
+def list_alerts(
+    status: str = Query(default="", description="Filter by status"),
+    severity: str = Query(default="", description="Filter by severity"),
+    rule_name: str = Query(default="", description="Filter by rule name"),
+    page_size: int = Query(default=50, ge=1, le=200),
+    page: int = Query(default=1, ge=1),
+):
+    query = {}
+    if status:
+        query["status"] = status
+    if severity:
+        query["severity"] = severity
+    if rule_name:
+        query["rule_name"] = {"$regex": rule_name, "$options": "i"}
+
+    total = alerts_collection.count_documents(query)
+    skip = (page - 1) * page_size
+    cursor = alerts_collection.find(query, {"_id": 0}).sort("timestamp", -1).skip(skip).limit(page_size)
+    return {"items": list(cursor), "total": total}
+
+
+@router.patch("/alerts/{alert_id}/status")
+def update_alert_status(alert_id: str, body: AlertStatusUpdate):
+    result = alerts_collection.update_one(
+        {"_id": ObjectId(alert_id)},
+        {"$set": {"status": body.status}},
+    )
+    if result.matched_count == 0:
+        raise HTTPException(status_code=404, detail="Alert not found")
+    return {"updated": True, "status": body.status}
+
+
+@router.get("/alerts/summary")
+def alert_summary():
+    """Return counts by status and severity for the dashboard."""
+    pipeline = [
+        {
+            "$group": {
+                "_id": {"status": "$status", "severity": "$severity"},
+                "count": {"$sum": 1},
+            }
+        }
+    ]
+    by_status_severity = list(alerts_collection.aggregate(pipeline))
+
+    total_open = alerts_collection.count_documents({"status": "open"})
+    total_acknowledged = alerts_collection.count_documents({"status": "acknowledged"})
+    total_resolved = alerts_collection.count_documents({"status": "resolved"})
+    total_false_positive = alerts_collection.count_documents({"status": "false_positive"})
+
+    return {
+        "total_open": total_open,
+        "total_acknowledged": total_acknowledged,
+        "total_resolved": total_resolved,
+        "total_false_positive": total_false_positive,
+        "by_status_severity": by_status_severity,
+    }