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>

frontend/src/types/index.ts

@@ -42,10 +42,20 @@ export interface Photo {
   url: string;
   thumbnail_url?: string;
   type: 'collage' | 'individual';
+  category_id?: number;
+  category_name?: string;
+  category_slug?: string;
   size: number;
   uploaded_at: string;
 }
 
+export interface PhotoCategory {
+  id: number;
+  name: string;
+  slug: string;
+  is_global: boolean;
+}
+
 export interface GalleryData {
   event: {
     id: number;
@@ -56,6 +66,7 @@ export interface GalleryData {
     color_theme?: string;
     expires_at: string;
   };
+  categories?: PhotoCategory[];
   photos: Photo[];
 }