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]>

backend/src/config/storage.js

@@ -0,0 +1,8 @@
+const path = require('path');
+
+// Get storage path from environment or default
+const getStoragePath = () => process.env.STORAGE_PATH || path.join(__dirname, '../../../storage');
+
+module.exports = {
+  getStoragePath
+};