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 <[email protected]>

frontend/src/services/toast.service.ts

@@ -0,0 +1,30 @@
+import { toast as toastify } from 'react-toastify';
+import i18n from '../i18n/config';
+
+export const toast = {
+  success: (messageKey: string, interpolations?: Record<string, any>) => {
+    const message = i18n.t(messageKey, interpolations);
+    toastify.success(message);
+  },
+  
+  error: (messageKey: string, interpolations?: Record<string, any>) => {
+    const message = i18n.t(messageKey, interpolations);
+    toastify.error(message);
+  },
+  
+  info: (messageKey: string, interpolations?: Record<string, any>) => {
+    const message = i18n.t(messageKey, interpolations);
+    toastify.info(message);
+  },
+  
+  warning: (messageKey: string, interpolations?: Record<string, any>) => {
+    const message = i18n.t(messageKey, interpolations);
+    toastify.warning(message);
+  },
+  
+  // For direct messages (not translation keys)
+  successDirect: (message: string) => toastify.success(message),
+  errorDirect: (message: string) => toastify.error(message),
+  infoDirect: (message: string) => toastify.info(message),
+  warningDirect: (message: string) => toastify.warning(message),
+};