perf(clickhouse): P0 dashboard/observability query limits, cache, slower polling

frontend/app/(main)/nodes/components/node-observability.tsx

@@ -289,7 +289,7 @@ export function NodeObservability({
   const observabilityQuery = useQuery({
     queryKey: ['openflare', 'node-observability', nodeId],
     queryFn: () => NodeService.getObservability(nodeId, { hours: 24, limit: 48 }),
-    refetchInterval: 10000,
+    refetchInterval: 30000,
   });
 
   const cleanupMutation = useMutation({

frontend/app/(main)/page.tsx

@@ -28,7 +28,7 @@ export default function OpenFlareDashboardPage() {
   const overviewQuery = useQuery({
     queryKey: dashboardQueryKey,
     queryFn: () => DashboardService.getOverview(),
-    refetchInterval: 30_000,
+    refetchInterval: 60_000,
   });
 
   const overview = overviewQuery.data;