Fix category management and remove import feature

- Fix category editing: Added GET /api/categories/:categoryId endpoint to fetch single category by ID, fixing 'Category not found' error when editing categories for active year
- Fix picks handling: Filter out picks for deleted categories when submitting, loading, and calculating scores to prevent errors
- Fix scores display: Always calculate scores from pickDetails instead of stored score value to ensure accuracy when categories are removed
- Add picks cleanup: Automatically clean up picks for deleted categories in database when categories are deleted or scores are fetched
- Fix winner clearing: Allow clearing winners by accepting empty/null winnerName in PUT /api/categories/:categoryId/winner
- Enable category number editing: Made category number editable in edit modal with validation and conflict checking; automatically updates all related picks when category number changes
- Add bulk category management: Added bulk select and delete functionality in Liste tab with select all checkbox and bulk delete button
- Remove import feature: Completely removed PDF/image import functionality including OCR, file upload, and all related UI components
- Update dependencies: Removed unused packages (tesseract.js, sharp, pdfjs-dist, canvas) after removing import feature
- Improve file cleanup: Added retry logic for file deletion to handle Windows file locking issues

public/user-stat.html

@@ -111,10 +111,9 @@
           <tr>
             <th scope="col">#</th>
             <th scope="col">Nom</th>
-            <th scope="col">Films</th>
+            <th scope="col" id="films-header">Films</th>
             <th scope="col" id="bon-picks-header">Bon picks</th>
-            <th scope="col">Points</th>
-            <th scope="col">Ratio</th>
+            <th scope="col" class="text-center">Points</th>
           </tr>
         </thead>
         <tbody id="user-table-body">