feat: Implement centralized audit logging admin interface (refs #10)

- Add audit_logs table with categories, severities, and indexes
- Create AuditLogService and AuditLogRepository
- Add REST API endpoints for viewing and exporting logs
- Wire audit logging into auth, vehicles, admin, and backup features
- Add desktop AdminLogsPage with filters and CSV export
- Add mobile AdminLogsMobileScreen with card layout
- Implement 90-day retention cleanup job
- Remove old AuditLogPanel from AdminCatalogPage

Security fixes:
- Escape LIKE special characters to prevent pattern injection
- Limit CSV export to 5000 records to prevent memory exhaustion
- Add truncation warning headers for large exports

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/admin/AdminCatalogPage.tsx

@@ -50,7 +50,6 @@ import {
 import { adminApi } from '../../features/admin/api/admin.api';
 import {
   AdminSectionHeader,
-  AuditLogPanel,
 } from '../../features/admin/components';
 import {
   CatalogSearchResult,
@@ -489,9 +488,6 @@ export const AdminCatalogPage: React.FC = () => {
         </Paper>
       )}
 
-      {/* Audit Log */}
-      <AuditLogPanel resourceType="catalog" />
-
       {/* Delete Confirmation Dialog */}
       <Dialog open={deleteDialogOpen} onClose={() => !deleting && setDeleteDialogOpen(false)}>
         <DialogTitle>