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/routes/publicSettings.js

@@ -5,9 +5,9 @@ const router = express.Router();
 // Get public settings (branding and theme)
 router.get('/', async (req, res) => {
   try {
-    // Fetch branding and theme settings
+    // Fetch branding, theme, and general settings
     const settings = await db('app_settings')
-      .whereIn('setting_type', ['branding', 'theme'])
+      .whereIn('setting_type', ['branding', 'theme', 'general'])
       .select('setting_key', 'setting_value');
     
     // Convert to object format
@@ -30,7 +30,14 @@ router.get('/', async (req, res) => {
       branding_support_email: settingsObject.branding_support_email || '',
       branding_footer_text: settingsObject.branding_footer_text || '',
       branding_watermark_enabled: settingsObject.branding_watermark_enabled || false,
-      theme_config: settingsObject.theme_config || null
+      branding_watermark_logo_url: settingsObject.branding_watermark_logo_url || '',
+      branding_watermark_position: settingsObject.branding_watermark_position || 'bottom-right',
+      branding_watermark_opacity: settingsObject.branding_watermark_opacity || 50,
+      branding_watermark_size: settingsObject.branding_watermark_size || 15,
+      branding_favicon_url: settingsObject.branding_favicon_url || '',
+      branding_logo_url: settingsObject.branding_logo_url || '',
+      theme_config: settingsObject.theme_config || null,
+      default_language: settingsObject.general_default_language || 'en'
     };
 
     res.json(publicSettings);