feat(i18n): Implement server-side internationalization support

- Added ServerI18nManager to handle translations and locale settings on the server.
- Integrated server-side translations into templates, reducing language flashing on initial load.
- Created API endpoints for setting and getting user language preferences.
- Enhanced client-side i18n handling to work seamlessly with server-rendered content.
- Updated various templates to utilize the new translation system.
- Added mixed i18n handler to coordinate server and client translations, improving user experience.
- Expanded translation files to include initialization messages for various components.

static/js/i18n/index.js

@@ -42,6 +42,11 @@ class I18nManager {
             return window.__INITIAL_LANGUAGE__;
         }
         
+        // 检查服务端传递的翻译数据
+        if (window.__SERVER_TRANSLATIONS__ && window.__SERVER_TRANSLATIONS__.language && this.locales[window.__SERVER_TRANSLATIONS__.language]) {
+            return window.__SERVER_TRANSLATIONS__.language;
+        }
+        
         // Check localStorage for user-selected language
         const STORAGE_PREFIX = 'lora_manager_';
         let userLanguage = null;