Fix gallery issues: user uploads, error messages, and translations

- Fix user upload feature not showing in gallery
  - Add allow_user_uploads and upload_category_id to auth response
  - These fields are required for the gallery to show the upload button

- Improve gallery login error messages
  - Add specific translations for wrong password vs rate limiting
  - Map backend error messages to user-friendly translations
  - Added auth.wrongPassword and auth.tooManyAttempts keys

- Gallery pages already have full translation support
  - GalleryPage and GalleryView use i18n properly
  - All text is translated based on selected language

These fixes resolve:
1. User upload button not showing even when enabled
2. Generic error messages for wrong passwords
3. No feedback for rate limiting

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

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

backend/src/routes/auth.js

@@ -115,7 +115,9 @@ router.post('/gallery/verify', [
         event_date: event.event_date,
         welcome_message: event.welcome_message,
         color_theme: event.color_theme,
-        expires_at: event.expires_at
+        expires_at: event.expires_at,
+        allow_user_uploads: event.allow_user_uploads,
+        upload_category_id: event.upload_category_id
       }
     });
   } catch (error) {