Fix language setting not being saved to database on admin settings page

- Added default_language field to general settings state in SettingsPage
- Replaced LanguageSelector component with simple select dropdown on settings page
- Fixed public settings endpoint to read general_default_language from database
- Language setting now properly saved when clicking Save Settings button
- Setting is correctly used by gallery login page and legal pages

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

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

backend/src/services/fileWatcher.js

@@ -60,12 +60,15 @@ async function processNewPhoto(filePath) {
   // Generate thumbnail
   const thumbnailPath = await generateThumbnail(filePath);
   
+  // Calculate relative thumbnail path
+  const relativeThumbPath = thumbnailPath; // thumbnailPath is already relative to storage root
+  
   // Add to database
   await db('photos').insert({
     event_id: event.id,
     filename: path.basename(filePath),
     path: relativePath,
-    thumbnail_path: thumbnailPath,
+    thumbnail_path: relativeThumbPath,
     type: photoType,
     size_bytes: stats.size
   });