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>

backend/src/features/audit-log/index.ts

@@ -0,0 +1,28 @@
+/**
+ * @ai-summary Audit log feature exports
+ * @ai-context Re-exports types, service, and repository for external use
+ */
+
+// Types
+export {
+  AuditLogCategory,
+  AuditLogSeverity,
+  AuditLogEntry,
+  CreateAuditLogInput,
+  AuditLogFilters,
+  AuditLogPagination,
+  AuditLogSearchResult,
+  AUDIT_LOG_CATEGORIES,
+  AUDIT_LOG_SEVERITIES,
+  isValidCategory,
+  isValidSeverity,
+} from './domain/audit-log.types';
+
+// Service
+export { AuditLogService } from './domain/audit-log.service';
+
+// Repository
+export { AuditLogRepository } from './data/audit-log.repository';
+
+// Singleton instance for cross-feature use
+export { auditLogService } from './audit-log.instance';