Fix critical issues: gallery authentication and photo duplication

- Fix gallery-specific authentication for images
  - Update AuthenticatedImage component to use gallery-specific tokens
  - Add isGallery prop to distinguish between admin and gallery contexts
  - Update PhotoGrid and PhotoLightbox to pass isGallery prop

- Fix photo duplication issue in fileWatcher service
  - Add check to prevent duplicate photo entries when backend restarts
  - File watcher now verifies if photo exists before inserting
  - Cleaned up 176 duplicate photos from database

These fixes resolve:
1. Gallery images not loading due to auth token errors
2. Photo count increasing without new uploads due to duplicates

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

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

frontend/src/components/gallery/PhotoGrid.tsx

@@ -237,6 +237,7 @@ const PhotoThumbnail: React.FC<PhotoThumbnailProps> = ({
             alt={photo.filename}
             className="w-full h-full object-cover rounded-lg transition-transform duration-200 group-hover:scale-105"
             loading="lazy"
+            isGallery={true}
           />
           
           {/* Overlay on hover */}