feat: Implement deals repository and routes for fetching best watched item prices

- Added a new DealsRepository class to interact with the database for fetching the best sale prices of watched items.
- Created a new route `/api/users/deals/best-watched-prices` to handle requests for the best prices of items the authenticated user is watching.
- Enhanced logging in the FlyerDataTransformer and FlyerProcessingService for better traceability.
- Updated tests to ensure proper logging and functionality in the FlyerProcessingService.
- Refactored logger client to support structured logging for better consistency across the application.

src/pages/admin/AdminStatsPage.tsx

@@ -37,7 +37,7 @@ export const AdminStatsPage: React.FC = () => {
                 setStats(data);
             } catch (err) {
                 const errorMessage = err instanceof Error ? err.message : 'An unknown error occurred.';
-                logger.error('Failed to fetch application stats', { error: err });
+                logger.error({ err }, 'Failed to fetch application stats');
                 setError(errorMessage);
             } finally {
                 setIsLoading(false);