fix: resolve gallery authentication and redirect issues

- Fix useWatermarkSettings hook to use public API endpoint instead of admin endpoint
- Add hero_photo_id to gallery authentication response
- Prevent 401 errors on gallery pages from redirecting to admin login
- Gallery pages now correctly fetch settings without requiring admin auth

The main issue was that gallery pages were calling admin-only endpoints
which triggered 401 errors and caused redirects to the admin login page.

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

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

backend/src/routes/auth.js

@@ -119,7 +119,8 @@ router.post('/gallery/verify', [
         color_theme: event.color_theme,
         expires_at: event.expires_at,
         allow_user_uploads: event.allow_user_uploads,
-        upload_category_id: event.upload_category_id
+        upload_category_id: event.upload_category_id,
+        hero_photo_id: event.hero_photo_id
       }
     });
   } catch (error) {