Implement Stage 3: Enhance content metadata and validation features

- Added entity metadata fields to the Tasks model, including entity_type, taxonomy, and cluster_role.
- Updated CandidateEngine to prioritize content relevance based on cluster mappings.
- Introduced metadata completeness scoring in ContentAnalyzer.
- Enhanced validation services to check for entity type and mapping completeness.
- Updated frontend components to display and validate new metadata fields.
- Implemented API endpoints for content validation and metadata persistence.
- Migrated existing data to populate new metadata fields for Tasks and Content.

frontend/src/layout/AppLayout.tsx

@@ -214,11 +214,20 @@ const LayoutContent: React.FC = () => {
       return;
     }
     
-    // Load balance if not already loaded
-    if (!balance && !useBillingStore.getState().loading) {
+    const billingState = useBillingStore.getState();
+    // Load balance if not already loaded and not currently loading
+    if (!balance && !billingState.loading) {
       loadBalance().catch((error) => {
         console.error('AppLayout: Error loading credit balance:', error);
         // Don't show error to user - balance is not critical for app functionality
+        // But retry after a delay
+        setTimeout(() => {
+          if (!useBillingStore.getState().balance && !useBillingStore.getState().loading) {
+            loadBalance().catch(() => {
+              // Silently fail on retry too
+            });
+          }
+        }, 5000);
       });
     }
   }, [isAuthenticated, balance, loadBalance, setMetrics]);
@@ -226,12 +235,18 @@ const LayoutContent: React.FC = () => {
   // Update header metrics when balance changes
   // This sets credit balance which will be merged with page metrics by HeaderMetricsContext
   useEffect(() => {
-    if (!isAuthenticated || !balance) {
-      // Clear credit balance but keep page metrics
+    if (!isAuthenticated) {
+      // Only clear metrics when not authenticated (user logged out)
       setMetrics([]);
       return;
     }
     
+    // If balance is null, don't clear metrics - let page metrics stay visible
+    // Only set credit metrics when balance is loaded
+    if (!balance) {
+      return;
+    }
+    
     // Determine accent color based on credit level
     let accentColor: 'blue' | 'green' | 'amber' | 'purple' = 'blue';
     if (balance.credits > 1000) {