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/services/cms.service.ts

@@ -0,0 +1,39 @@
+import { api } from '../config/api';
+
+export interface CMSPage {
+  id: number;
+  slug: string;
+  title_en: string;
+  title_de: string;
+  content_en: string;
+  content_de: string;
+  updated_at: string;
+}
+
+export const cmsService = {
+  // Get all CMS pages
+  async getPages(): Promise<CMSPage[]> {
+    const response = await api.get<CMSPage[]>('/api/admin/cms/pages');
+    return response.data;
+  },
+
+  // Get a single CMS page
+  async getPage(slug: string): Promise<CMSPage> {
+    const response = await api.get<CMSPage>(`/api/admin/cms/pages/${slug}`);
+    return response.data;
+  },
+
+  // Update a CMS page
+  async updatePage(slug: string, data: Partial<CMSPage>): Promise<CMSPage> {
+    const response = await api.put<CMSPage>(`/api/admin/cms/pages/${slug}`, data);
+    return response.data;
+  },
+
+  // Get public CMS page (no auth required)
+  async getPublicPage(slug: string, lang: string = 'en'): Promise<{ title: string; content: string }> {
+    const response = await api.get<{ title: string; content: string }>(`/api/public/pages/${slug}`, {
+      params: { lang }
+    });
+    return response.data;
+  }
+};