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_en.arb

@@ -83,8 +83,7 @@
   "settingsSectionPrivacy": "Privacy",
   "settingsSectionNotification": "Notification Settings",
   "settingsAccountAndDataTitle": "Account Data",
-  "settingsInterfaceLanguage": "Interface Language",
-  "settingsAiLanguage": "AI Response Language",
+  "settingsLanguage": "Language",
   "settingsNotificationAllow": "Allow Notifications",
   "settingsNotificationVibration": "Allow Vibration",
   "settingsSectionAbout": "About",
@@ -111,12 +110,8 @@
     }
   },
   "settingsCoinHeroSubtitle": "Credits will be used for casting and related services later.",
-  "settingsAiLanguage": "AI Response Language",
-  "settingsAiLanguageHint": "This field will align with profiles.settings.preferences.ai_language once the real preference flow is connected.",
   "settingsTimezone": "Time Zone",
   "settingsTimezoneHint": "This field will align with profiles.settings.preferences.timezone and later provide a real time zone picker.",
-  "settingsCountry": "Country/Region",
-  "settingsCountryHint": "This field will align with profiles.settings.preferences.country and later provide a region picker.",
   "settingsPrivacyProfileVisibility": "Profile Visibility",
   "settingsPrivacyPersonalization": "Personalization",
   "settingsPrivacyHistoryVisibility": "History Visibility",
@@ -195,6 +190,7 @@
   "settingsCoinPackPopular": "Popular Pack",
   "settingsCoinPackPremium": "Premium Pack",
   "settingsCoinPackPopularBadge": "Popular",
+  "settingsCoinPackNewUserBadge": "Only Once",
   "settingsPurchaseButton": "Pay Now",
   "settingsPurchasePending": "",
   "settingsCoinAmount": "{amount} credits",
@@ -511,5 +507,51 @@
   "paymentProductNotFound": "Product temporarily unavailable",
   "paymentStarterPackIneligible": "Starter pack is limited to one purchase per user",
   "paymentProductUnavailable": "Product temporarily unavailable",
-  "paymentPending": "Apple is processing, please wait"
+  "paymentPending": "Apple is processing, please wait",
+  "notifyCenterTitle": "Notifications",
+  "notifyMarkAllRead": "Mark all read",
+  "notifyLoadFailed": "Failed to load",
+  "notifyRetry": "Retry",
+  "notifyEmpty": "No notifications",
+  "timeJustNow": "Just now",
+  "timeMinutesAgo": "{minutes}m ago",
+  "@timeMinutesAgo": {
+    "placeholders": {
+      "minutes": {
+        "type": "int"
+      }
+    }
+  },
+  "timeHoursAgo": "{hours}h ago",
+  "@timeHoursAgo": {
+    "placeholders": {
+      "hours": {
+        "type": "int"
+      }
+    }
+  },
+  "timeDaysAgo": "{days}d ago",
+  "@timeDaysAgo": {
+    "placeholders": {
+      "days": {
+        "type": "int"
+      }
+    }
+  },
+  "pointsLedgerTitle": "Points Ledger",
+  "pointsLedgerEmpty": "No records yet",
+  "pointsLedgerTypeRegister": "Registration bonus",
+  "pointsLedgerTypePurchase": "Purchase credits",
+  "pointsLedgerTypeConsume": "AI chat cost",
+  "pointsLedgerTypeAdjust": "System adjustment",
+  "pointsLedgerTypeRefund": "Refund",
+  "pointsLedgerBalance": "Balance {balance}",
+  "@pointsLedgerBalance": {
+    "placeholders": {
+      "balance": {
+        "type": "int"
+      }
+    }
+  },
+  "retry": "Retry"
 }