Add visibility toggle for picks features and rename Mes choix to Mes picks

- Renamed 'Mes choix' to 'Mes picks' across all pages and JavaScript files
- Added visibility toggle in control panel (Réglages > Visibilité) to control:
  - Display of 'Mes picks' button in navigation
  - Display of 'Bon picks' column in user statistics
- Combined both visibility options into single toggle for simplicity
- Added backend API endpoints for visibility configuration
- Implemented localStorage caching for instant visibility updates
- Fixed flash of content issues when navigating between pages
- Updated stats endpoint to calculate correct picks on-the-fly from current winners
- Renamed 'Bonnes réponses' to 'Bon picks' in user statistics table

public/movies.html

@@ -59,7 +59,7 @@
         <a href="movies.html" class="nav-link btn btn-outline-light me-2">Films</a>
         <a href="checklist.html" class="nav-link btn btn-outline-light me-2">Checklist</a>
         <a href="user-stat.html" class="nav-link btn btn-outline-light me-2">Statistiques</a>
-        <a href="picks.html" class="nav-link btn btn-outline-light me-2">Mes choix</a>
+        <a href="picks.html" class="nav-link btn btn-outline-light me-2" id="nav-link-picks" style="display: none;">Mes picks</a>
         <a id="admin-control-link" href="control.html" class="nav-link btn btn-warning me-2 d-none">Admin</a>
       </div>
       <!-- Move user info inside collapsible navbar and align it properly -->