Fix TypeScript compilation errors in frontend components

- Remove unused variables in ApplicationInfo, ArchitectureDebugPage
- Fix type errors in Dashboard, GovernanceAnalysis, GovernanceModelHelper (PageHeader description prop)
- Add null checks and explicit types in DataValidationDashboard
- Fix ObjectDetailModal type errors for _jiraCreatedAt and Date constructor
- Remove unused imports and variables in SchemaConfigurationSettings
- Update PageHeader to accept string | ReactNode for description prop

frontend/src/components/ArchitectureDebugPage.tsx

@@ -168,7 +168,7 @@ export default function ArchitectureDebugPage() {
       const referencedObjectKey = inputs.referencedObjectKey || (() => {
         // Try to find a reference in the object
         const references: string[] = [];
-        for (const [key, value] of Object.entries(sampleObject)) {
+        for (const [, value] of Object.entries(sampleObject)) {
           if (value && typeof value === 'object' && ('objectKey' in value || 'key' in value)) {
             const objKey = (value as any).objectKey || (value as any).key;
             if (objKey) references.push(objKey);
@@ -288,7 +288,7 @@ export default function ArchitectureDebugPage() {
         credentials: 'include',
       });
       if (!syncResponse.ok) throw new Error('Sync failed');
-      const syncResult = await syncResponse.json();
+      await syncResponse.json();
 
       // Step 3: Check final count (should not have increased much)
       updateTestResult(testId, { message: 'Checking final object count...' });
@@ -506,7 +506,7 @@ export default function ArchitectureDebugPage() {
         const error = await updateResponse.json();
         throw new Error(error.error || 'Update failed');
       }
-      const updateResult = await updateResponse.json();
+      await updateResponse.json();
 
       // Step 3: Immediately check DB (without refresh)
       updateTestResult(testId, { message: 'Checking DB state immediately...' });