fix: Implement gallery-specific authentication tokens

- Fix issue where different galleries shared authentication
- Store gallery tokens with slug-specific keys in localStorage
- Remove global gallery_token cookie approach
- Each gallery now maintains its own authentication state
- Add cleanup for legacy authentication data

This ensures that accessing different galleries requires separate authentication
and prevents cross-gallery authentication leakage.

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

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

frontend/src/services/auth.service.ts

@@ -28,11 +28,11 @@ export const authService = {
       recaptchaToken
     });
     
-    setAuthToken(response.data.token, false);
+    // Token is now handled by GalleryAuthContext with slug-specific storage
     return response.data;
   },
 
   galleryLogout() {
-    clearAuthToken(false);
+    // Logout is now handled by GalleryAuthContext
   },
 };