feat: block official provider switching during proxy takeover

Prevent users from switching to official providers (Anthropic/OpenAI/Google)
when proxy takeover is active, as using a proxy with official APIs may cause
account bans.

Defense-in-depth across 4 layers:
- Backend: ProviderService::switch(), hot_switch_provider(), switch_proxy_provider command
- Frontend: useProviderActions soft guard with error toast
- UI: ProviderActions button disabled with ShieldAlert icon
- Tray menu: official provider items disabled with ⛔ indicator

Also warns when enabling proxy takeover while current provider is official.

src/i18n/locales/en.json

@@ -108,6 +108,7 @@
     "currentlyUsing": "Currently Using",
     "enable": "Enable",
     "inUse": "In Use",
+    "blockedByProxy": "Blocked",
     "editProvider": "Edit Provider",
     "editProviderHint": "Configuration will be applied to the current provider immediately after update.",
     "deleteProvider": "Delete Provider",
@@ -206,7 +207,9 @@
     "openclawDefaultModelSetFailed": "Failed to set default model",
     "openclawNoModels": "No models configured",
     "backfillWarning": "Switched successfully, but failed to save changes back to the previous provider",
-    "windowControlFailed": "Window control failed: {{error}}"
+    "windowControlFailed": "Window control failed: {{error}}",
+    "officialBlockedByProxy": "Cannot switch to official provider while proxy takeover is active. Using proxy with official APIs may cause account bans.",
+    "proxyOfficialWarning": "Current provider {{name}} is official. Consider switching to a third-party provider before using proxy takeover."
   },
   "confirm": {
     "deleteProvider": "Delete Provider",

src/i18n/locales/ja.json

@@ -108,6 +108,7 @@
     "currentlyUsing": "現在使用中",
     "enable": "有効化",
     "inUse": "使用中",
+    "blockedByProxy": "ブロック",
     "editProvider": "プロバイダーを編集",
     "editProviderHint": "保存すると現在のプロバイダーにすぐ反映されます。",
     "deleteProvider": "プロバイダーを削除",
@@ -206,7 +207,9 @@
     "openclawDefaultModelSetFailed": "デフォルトモデルの設定に失敗しました",
     "openclawNoModels": "モデルが設定されていません",
     "backfillWarning": "切り替え成功しましたが、前のプロバイダーへの設定保存に失敗しました",
-    "windowControlFailed": "ウィンドウ操作に失敗しました: {{error}}"
+    "windowControlFailed": "ウィンドウ操作に失敗しました: {{error}}",
+    "officialBlockedByProxy": "プロキシ接管モード中は公式プロバイダーに切り替えできません。プロキシ経由で公式 API にアクセスするとアカウントが停止される可能性があります。",
+    "proxyOfficialWarning": "現在のプロバイダー {{name}} は公式です。プロキシ接管を使用する前にサードパーティプロバイダーに切り替えてください。"
   },
   "confirm": {
     "deleteProvider": "プロバイダーを削除",

src/i18n/locales/zh.json

@@ -108,6 +108,7 @@
     "currentlyUsing": "当前使用",
     "enable": "启用",
     "inUse": "使用中",
+    "blockedByProxy": "已拦截",
     "editProvider": "编辑供应商",
     "editProviderHint": "更新配置后将立即应用到当前供应商。",
     "deleteProvider": "删除供应商",
@@ -206,7 +207,9 @@
     "openclawDefaultModelSetFailed": "设置默认模型失败",
     "openclawNoModels": "该供应商没有配置模型",
     "backfillWarning": "切换成功，但旧供应商配置回填失败，您手动修改的配置可能未保存",
-    "windowControlFailed": "窗口控制失败：{{error}}"
+    "windowControlFailed": "窗口控制失败：{{error}}",
+    "officialBlockedByProxy": "代理接管模式下不能切换到官方供应商，使用代理访问官方 API 可能导致账号被封禁",
+    "proxyOfficialWarning": "当前供应商 {{name}} 是官方供应商，建议切换到第三方供应商后再使用代理接管"
   },
   "confirm": {
     "deleteProvider": "删除供应商",