Fix gallery login errors and photo upload issues

- Fix photo upload cross-device link error
  - Changed fs.rename to fs.copyFile + fs.unlink to handle Docker volume mounts
  - This fixes EXDEV errors when uploading photos from /tmp to storage

- Improve gallery login error handling
  - Add console logging for debugging
  - Prevent form refresh with stopPropagation
  - Show specific error messages based on status codes
  - Keep password field populated on error for retry
  - Map 404 to gallery not found message

- Enhanced upload error messages
  - Show specific error message for each failed file
  - Display backend error messages in toast notifications

These fixes resolve:
1. Photo uploads failing silently with cross-device link errors
2. Login errors not displaying and form refreshing
3. Upload errors not showing user-friendly messages

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

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

frontend/src/components/gallery/UserPhotoUpload.tsx

@@ -78,9 +78,13 @@ export const UserPhotoUpload: React.FC<UserPhotoUploadProps> = ({
           },
         });
         successCount++;
-      } catch (error) {
+      } catch (error: any) {
         console.error(`Failed to upload ${file.name}:`, error);
         failedCount++;
+        
+        // Show specific error message
+        const errorMessage = error.response?.data?.error || error.message || 'Upload failed';
+        toast.error(`${file.name}: ${errorMessage}`);
       }
     }