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.dart

@@ -513,17 +513,11 @@ abstract class AppLocalizations {
   /// **'账号数据'**
   String get settingsAccountAndDataTitle;
 
-  /// No description provided for @settingsInterfaceLanguage.
+  /// No description provided for @settingsLanguage.
   ///
   /// In zh, this message translates to:
-  /// **'界面语言'**
-  String get settingsInterfaceLanguage;
-
-  /// No description provided for @settingsAiLanguage.
-  ///
-  /// In zh, this message translates to:
-  /// **'AI 回复语言'**
-  String get settingsAiLanguage;
+  /// **'语言'**
+  String get settingsLanguage;
 
   /// No description provided for @settingsNotificationAllow.
   ///
@@ -597,12 +591,6 @@ abstract class AppLocalizations {
   /// **'点数可用于后续起卦与相关服务消费'**
   String get settingsCoinHeroSubtitle;
 
-  /// No description provided for @settingsAiLanguageHint.
-  ///
-  /// In zh, this message translates to:
-  /// **'该字段将对齐 profiles.settings.preferences.ai_language，后续接入真实偏好设置。'**
-  String get settingsAiLanguageHint;
-
   /// No description provided for @settingsTimezone.
   ///
   /// In zh, this message translates to:
@@ -615,18 +603,6 @@ abstract class AppLocalizations {
   /// **'该字段将对齐 profiles.settings.preferences.timezone，后续提供时区选择。'**
   String get settingsTimezoneHint;
 
-  /// No description provided for @settingsCountry.
-  ///
-  /// In zh, this message translates to:
-  /// **'国家/地区'**
-  String get settingsCountry;
-
-  /// No description provided for @settingsCountryHint.
-  ///
-  /// In zh, this message translates to:
-  /// **'该字段将对齐 profiles.settings.preferences.country，后续提供国家或地区选择。'**
-  String get settingsCountryHint;
-
   /// No description provided for @settingsPrivacyProfileVisibility.
   ///
   /// In zh, this message translates to:
@@ -969,6 +945,12 @@ abstract class AppLocalizations {
   /// **'推荐'**
   String get settingsCoinPackPopularBadge;
 
+  /// No description provided for @settingsCoinPackNewUserBadge.
+  ///
+  /// In zh, this message translates to:
+  /// **'限购一次'**
+  String get settingsCoinPackNewUserBadge;
+
   /// No description provided for @settingsPurchaseButton.
   ///
   /// In zh, this message translates to:
@@ -2468,6 +2450,114 @@ abstract class AppLocalizations {
   /// In zh, this message translates to:
   /// **'Apple 正在处理中，请稍候'**
   String get paymentPending;
+
+  /// No description provided for @notifyCenterTitle.
+  ///
+  /// In zh, this message translates to:
+  /// **'通知'**
+  String get notifyCenterTitle;
+
+  /// No description provided for @notifyMarkAllRead.
+  ///
+  /// In zh, this message translates to:
+  /// **'全部已读'**
+  String get notifyMarkAllRead;
+
+  /// No description provided for @notifyLoadFailed.
+  ///
+  /// In zh, this message translates to:
+  /// **'加载失败'**
+  String get notifyLoadFailed;
+
+  /// No description provided for @notifyRetry.
+  ///
+  /// In zh, this message translates to:
+  /// **'重试'**
+  String get notifyRetry;
+
+  /// No description provided for @notifyEmpty.
+  ///
+  /// In zh, this message translates to:
+  /// **'暂无通知'**
+  String get notifyEmpty;
+
+  /// No description provided for @timeJustNow.
+  ///
+  /// In zh, this message translates to:
+  /// **'刚刚'**
+  String get timeJustNow;
+
+  /// No description provided for @timeMinutesAgo.
+  ///
+  /// In zh, this message translates to:
+  /// **'{minutes}分钟前'**
+  String timeMinutesAgo(int minutes);
+
+  /// No description provided for @timeHoursAgo.
+  ///
+  /// In zh, this message translates to:
+  /// **'{hours}小时前'**
+  String timeHoursAgo(int hours);
+
+  /// No description provided for @timeDaysAgo.
+  ///
+  /// In zh, this message translates to:
+  /// **'{days}天前'**
+  String timeDaysAgo(int days);
+
+  /// No description provided for @pointsLedgerTitle.
+  ///
+  /// In zh, this message translates to:
+  /// **'积分流水'**
+  String get pointsLedgerTitle;
+
+  /// No description provided for @pointsLedgerEmpty.
+  ///
+  /// In zh, this message translates to:
+  /// **'暂无流水记录'**
+  String get pointsLedgerEmpty;
+
+  /// No description provided for @pointsLedgerTypeRegister.
+  ///
+  /// In zh, this message translates to:
+  /// **'注册赠送'**
+  String get pointsLedgerTypeRegister;
+
+  /// No description provided for @pointsLedgerTypePurchase.
+  ///
+  /// In zh, this message translates to:
+  /// **'购买积分包'**
+  String get pointsLedgerTypePurchase;
+
+  /// No description provided for @pointsLedgerTypeConsume.
+  ///
+  /// In zh, this message translates to:
+  /// **'AI 对话消耗'**
+  String get pointsLedgerTypeConsume;
+
+  /// No description provided for @pointsLedgerTypeAdjust.
+  ///
+  /// In zh, this message translates to:
+  /// **'系统调整'**
+  String get pointsLedgerTypeAdjust;
+
+  /// No description provided for @pointsLedgerTypeRefund.
+  ///
+  /// In zh, this message translates to:
+  /// **'退款'**
+  String get pointsLedgerTypeRefund;
+
+  /// No description provided for @pointsLedgerBalance.
+  ///
+  /// In zh, this message translates to:
+  /// **'余额 {balance}'**
+  String pointsLedgerBalance(int balance);
+
+  /// No description provided for @retry.
+  ///
+  /// In zh, this message translates to:
+  /// **'重试'**
+  String get retry;
 }
 
 class _AppLocalizationsDelegate