feat: implement Phase 3 scaling

- Replace skip-based pagination with cursor-based pagination (timestamp|_id cursors)
- Add Prometheus /metrics endpoint with request latency, fetch volume, and error counters
- Implement incremental fetch watermarking per source (watermarks collection in MongoDB)
- Add Graph change notification webhook endpoint (/api/webhooks/graph)
- Add correlation ID middleware for distributed tracing (x-request-id header)
- Update frontend to use cursor-based pagination with Prev/Next navigation
- Update tests for cursor pagination, metrics, webhooks, and watermark mocking

backend/sources/intune_audit.py

@@ -4,13 +4,13 @@ from graph.auth import get_access_token
 from utils.http import get_with_retry
 
 
-def fetch_intune_audit(hours: int = 24, max_pages: int = 50) -> list[dict]:
+def fetch_intune_audit(hours: int = 24, since: str | None = None, max_pages: int = 50) -> list[dict]:
     """
     Fetch Intune audit events via Microsoft Graph.
     Requires Intune audit permissions (e.g., DeviceManagementConfiguration.Read.All).
     """
     token = get_access_token()
-    start_time = (datetime.utcnow() - timedelta(hours=hours)).isoformat() + "Z"
+    start_time = since or (datetime.utcnow() - timedelta(hours=hours)).isoformat() + "Z"
     url = (
         "https://graph.microsoft.com/v1.0/deviceManagement/auditEvents"
         f"?$filter=activityDateTime ge {start_time}"