feat(i18n): add backend multi-language support with user language preference

- Add go-i18n library for internationalization
- Create i18n package with translation keys and YAML locale files (zh/en)
- Implement i18n middleware for language detection from user settings and Accept-Language header
- Add Language field to UserSetting DTO
- Update API response helpers with i18n support (ApiErrorI18n, ApiSuccessI18n)
- Migrate hardcoded messages in token, redemption, and user controllers
- Add frontend language preference settings component
- Sync language preference across header selector and user settings
- Auto-restore user language preference on login

web/src/components/settings/PersonalSetting.jsx

@@ -39,6 +39,7 @@ import { useTranslation } from 'react-i18next';
 import UserInfoHeader from './personal/components/UserInfoHeader';
 import AccountManagement from './personal/cards/AccountManagement';
 import NotificationSettings from './personal/cards/NotificationSettings';
+import PreferencesSettings from './personal/cards/PreferencesSettings';
 import CheckinCalendar from './personal/cards/CheckinCalendar';
 import EmailBindModal from './personal/modals/EmailBindModal';
 import WeChatBindModal from './personal/modals/WeChatBindModal';
@@ -463,24 +464,29 @@ const PersonalSetting = () => {
           {/* 账户管理和其他设置 */}
           <div className='grid grid-cols-1 xl:grid-cols-2 items-start gap-4 md:gap-6 mt-4 md:mt-6'>
             {/* 左侧：账户管理设置 */}
-            <AccountManagement
-              t={t}
-              userState={userState}
-              status={status}
-              systemToken={systemToken}
-              setShowEmailBindModal={setShowEmailBindModal}
-              setShowWeChatBindModal={setShowWeChatBindModal}
-              generateAccessToken={generateAccessToken}
-              handleSystemTokenClick={handleSystemTokenClick}
-              setShowChangePasswordModal={setShowChangePasswordModal}
-              setShowAccountDeleteModal={setShowAccountDeleteModal}
-              passkeyStatus={passkeyStatus}
-              passkeySupported={passkeySupported}
-              passkeyRegisterLoading={passkeyRegisterLoading}
-              passkeyDeleteLoading={passkeyDeleteLoading}
-              onPasskeyRegister={handleRegisterPasskey}
-              onPasskeyDelete={handleRemovePasskey}
-            />
+            <div className='flex flex-col gap-4 md:gap-6'>
+              <AccountManagement
+                t={t}
+                userState={userState}
+                status={status}
+                systemToken={systemToken}
+                setShowEmailBindModal={setShowEmailBindModal}
+                setShowWeChatBindModal={setShowWeChatBindModal}
+                generateAccessToken={generateAccessToken}
+                handleSystemTokenClick={handleSystemTokenClick}
+                setShowChangePasswordModal={setShowChangePasswordModal}
+                setShowAccountDeleteModal={setShowAccountDeleteModal}
+                passkeyStatus={passkeyStatus}
+                passkeySupported={passkeySupported}
+                passkeyRegisterLoading={passkeyRegisterLoading}
+                passkeyDeleteLoading={passkeyDeleteLoading}
+                onPasskeyRegister={handleRegisterPasskey}
+                onPasskeyDelete={handleRemovePasskey}
+              />
+
+              {/* 偏好设置（语言等） */}
+              <PreferencesSettings t={t} />
+            </div>
 
             {/* 右侧：其他设置 */}
             <NotificationSettings