Add automated data retention cleanup

Implements edge function, Django tasks, and UI hooks/panels for automatic retention of old metrics, anomalies, alerts, and incidents, plus updates to query keys and monitoring dashboard to reflect data-retention workflows.

src/lib/queryKeys.ts

@@ -96,5 +96,6 @@ export const queryKeys = {
     incidents: (status?: string) => ['monitoring', 'incidents', status] as const,
     incidentDetails: (incidentId: string) => ['monitoring', 'incident-details', incidentId] as const,
     anomalyDetections: () => ['monitoring', 'anomaly-detections'] as const,
+    dataRetentionStats: () => ['monitoring', 'data-retention-stats'] as const,
   },
 } as const;