feat(claude): show proxy hint when switching to OpenAI Chat format provider

Display an info toast when switching to a provider that uses OpenAI Chat
format (apiFormat === "openai_chat"), reminding users to enable the proxy
service. Move toast logic from mutation to useProviderActions for better
control over notification content based on provider properties.

src/i18n/locales/en.json

@@ -155,7 +155,8 @@
     "deleteSuccess": "Provider deleted",
     "deleteFailed": "Failed to delete provider: {{error}}",
     "settingsSaved": "Settings saved",
-    "settingsSaveFailed": "Failed to save settings: {{error}}"
+    "settingsSaveFailed": "Failed to save settings: {{error}}",
+    "openAIChatFormatHint": "This provider uses OpenAI Chat format and requires the proxy service to be enabled"
   },
   "confirm": {
     "deleteProvider": "Delete Provider",

src/i18n/locales/ja.json

@@ -155,7 +155,8 @@
     "deleteSuccess": "プロバイダーを削除しました",
     "deleteFailed": "プロバイダーの削除に失敗しました: {{error}}",
     "settingsSaved": "設定を保存しました",
-    "settingsSaveFailed": "設定の保存に失敗しました: {{error}}"
+    "settingsSaveFailed": "設定の保存に失敗しました: {{error}}",
+    "openAIChatFormatHint": "このプロバイダーは OpenAI Chat フォーマットを使用しており、プロキシサービスの有効化が必要です"
   },
   "confirm": {
     "deleteProvider": "プロバイダーを削除",

src/i18n/locales/zh.json

@@ -155,7 +155,8 @@
     "deleteSuccess": "供应商已删除",
     "deleteFailed": "删除供应商失败：{{error}}",
     "settingsSaved": "设置已保存",
-    "settingsSaveFailed": "保存设置失败：{{error}}"
+    "settingsSaveFailed": "保存设置失败：{{error}}",
+    "openAIChatFormatHint": "此供应商使用 OpenAI Chat 格式，需要开启代理服务才能正常使用"
   },
   "confirm": {
     "deleteProvider": "删除供应商",