refactor(settings): 统一语言设置，合并 interface_language 和 ai_language

- 后端 Schema 将 interface_language 和 ai_language 合并为 language
- 前端设置界面只保留一个语言选项
- AI 回复语言统一使用 language 设置
- 更新协议文档
- 新增数据库迁移脚本

apps/lib/l10n/app_localizations_zh.dart

@@ -224,10 +224,7 @@ class AppLocalizationsZh extends AppLocalizations {
   String get settingsAccountAndDataTitle => '账号数据';
 
   @override
-  String get settingsInterfaceLanguage => '界面语言';
-
-  @override
-  String get settingsAiLanguage => 'AI 回复语言';
+  String get settingsLanguage => '语言';
 
   @override
   String get settingsNotificationAllow => '允许通知';
@@ -270,10 +267,6 @@ class AppLocalizationsZh extends AppLocalizations {
   @override
   String get settingsCoinHeroSubtitle => '点数可用于后续起卦与相关服务消费';
 
-  @override
-  String get settingsAiLanguageHint =>
-      '该字段将对齐 profiles.settings.preferences.ai_language，后续接入真实偏好设置。';
-
   @override
   String get settingsTimezone => '时区';
 
@@ -281,13 +274,6 @@ class AppLocalizationsZh extends AppLocalizations {
   String get settingsTimezoneHint =>
       '该字段将对齐 profiles.settings.preferences.timezone，后续提供时区选择。';
 
-  @override
-  String get settingsCountry => '国家/地区';
-
-  @override
-  String get settingsCountryHint =>
-      '该字段将对齐 profiles.settings.preferences.country，后续提供国家或地区选择。';
-
   @override
   String get settingsPrivacyProfileVisibility => '资料可见性';
 
@@ -469,6 +455,9 @@ class AppLocalizationsZh extends AppLocalizations {
   @override
   String get settingsCoinPackPopularBadge => '推荐';
 
+  @override
+  String get settingsCoinPackNewUserBadge => '限购一次';
+
   @override
   String get settingsPurchaseButton => '立即支付';
 
@@ -1243,6 +1232,68 @@ class AppLocalizationsZh extends AppLocalizations {
 
   @override
   String get paymentPending => 'Apple 正在处理中，请稍候';
+
+  @override
+  String get notifyCenterTitle => '通知';
+
+  @override
+  String get notifyMarkAllRead => '全部已读';
+
+  @override
+  String get notifyLoadFailed => '加载失败';
+
+  @override
+  String get notifyRetry => '重试';
+
+  @override
+  String get notifyEmpty => '暂无通知';
+
+  @override
+  String get timeJustNow => '刚刚';
+
+  @override
+  String timeMinutesAgo(int minutes) {
+    return '$minutes分钟前';
+  }
+
+  @override
+  String timeHoursAgo(int hours) {
+    return '$hours小时前';
+  }
+
+  @override
+  String timeDaysAgo(int days) {
+    return '$days天前';
+  }
+
+  @override
+  String get pointsLedgerTitle => '积分流水';
+
+  @override
+  String get pointsLedgerEmpty => '暂无流水记录';
+
+  @override
+  String get pointsLedgerTypeRegister => '注册赠送';
+
+  @override
+  String get pointsLedgerTypePurchase => '购买积分包';
+
+  @override
+  String get pointsLedgerTypeConsume => 'AI 对话消耗';
+
+  @override
+  String get pointsLedgerTypeAdjust => '系统调整';
+
+  @override
+  String get pointsLedgerTypeRefund => '退款';
+
+  @override
+  String pointsLedgerBalance(int balance) {
+    return '余额 $balance';
+  }
+
+  @override
+  String get retry => '重试';
 }
 
 /// The translations for Chinese, using the Han script (`zh_Hant`).
@@ -1397,10 +1448,7 @@ class AppLocalizationsZhHant extends AppLocalizationsZh {
   String get settingsAccountAndDataTitle => '帳號資料';
 
   @override
-  String get settingsInterfaceLanguage => '介面語言';
-
-  @override
-  String get settingsAiLanguage => 'AI 回覆語言';
+  String get settingsLanguage => '語言';
 
   @override
   String get settingsNotificationAllow => '允許通知';
@@ -1562,6 +1610,9 @@ class AppLocalizationsZhHant extends AppLocalizationsZh {
   @override
   String get settingsCoinPackPopularBadge => '推薦';
 
+  @override
+  String get settingsCoinPackNewUserBadge => '限購一次';
+
   @override
   String get settingsPurchaseButton => '立即支付';
 
@@ -2240,4 +2291,66 @@ class AppLocalizationsZhHant extends AppLocalizationsZh {
 
   @override
   String get paymentPending => 'Apple 正在處理中，請稍候';
+
+  @override
+  String get notifyCenterTitle => '通知';
+
+  @override
+  String get notifyMarkAllRead => '全部已讀';
+
+  @override
+  String get notifyLoadFailed => '載入失敗';
+
+  @override
+  String get notifyRetry => '重試';
+
+  @override
+  String get notifyEmpty => '暫無通知';
+
+  @override
+  String get timeJustNow => '剛剛';
+
+  @override
+  String timeMinutesAgo(int minutes) {
+    return '$minutes分鐘前';
+  }
+
+  @override
+  String timeHoursAgo(int hours) {
+    return '$hours小時前';
+  }
+
+  @override
+  String timeDaysAgo(int days) {
+    return '$days天前';
+  }
+
+  @override
+  String get pointsLedgerTitle => '積分流水';
+
+  @override
+  String get pointsLedgerEmpty => '暫無流水記錄';
+
+  @override
+  String get pointsLedgerTypeRegister => '註冊贈送';
+
+  @override
+  String get pointsLedgerTypePurchase => '購買積分包';
+
+  @override
+  String get pointsLedgerTypeConsume => 'AI 對話消耗';
+
+  @override
+  String get pointsLedgerTypeAdjust => '系統調整';
+
+  @override
+  String get pointsLedgerTypeRefund => '退款';
+
+  @override
+  String pointsLedgerBalance(int balance) {
+    return '餘額 $balance';
+  }
+
+  @override
+  String get retry => '重試';
 }