feat(openclaw): add default model button and fix sessionsApi export

- Add "Enable as Default" button to OpenClaw provider cards
- Place enable button before add/remove button for better UX
- Disable remove button when provider is set as default
- Add sessionsApi re-export from api barrel file to fix white screen
- Add i18n keys for default model feature (zh/en/ja)

src/i18n/locales/en.json

@@ -88,6 +88,8 @@
     "addOpenCodeProvider": "Add OpenCode Provider",
     "addToConfig": "Add",
     "removeFromConfig": "Remove",
+    "setAsDefault": "Enable",
+    "isDefault": "Default",
     "inConfig": "Added",
     "addProviderHint": "Fill in the information to quickly switch providers in the list.",
     "editClaudeProvider": "Edit Claude Code Provider",
@@ -163,7 +165,10 @@
     "settingsSaveFailed": "Failed to save settings: {{error}}",
     "openAIChatFormatHint": "This provider uses OpenAI Chat format and requires the proxy service to be enabled",
     "openLinkFailed": "Failed to open link",
-    "openclawModelsRegistered": "Models have been registered to /model list"
+    "openclawModelsRegistered": "Models have been registered to /model list",
+    "openclawDefaultModelSet": "Set as default model",
+    "openclawDefaultModelSetFailed": "Failed to set default model",
+    "openclawNoModels": "No models configured"
   },
   "confirm": {
     "deleteProvider": "Delete Provider",

src/i18n/locales/ja.json

@@ -88,6 +88,8 @@
     "addOpenCodeProvider": "OpenCode プロバイダーを追加",
     "addToConfig": "追加",
     "removeFromConfig": "削除",
+    "setAsDefault": "有効化",
+    "isDefault": "デフォルト",
     "inConfig": "追加済み",
     "addProviderHint": "一覧にすばやく切り替えられるよう、ここに情報を入力してください。",
     "editClaudeProvider": "Claude Code プロバイダーを編集",
@@ -163,7 +165,10 @@
     "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",
     "openLinkFailed": "リンクを開けませんでした",
-    "openclawModelsRegistered": "モデルが /model リストに登録されました"
+    "openclawModelsRegistered": "モデルが /model リストに登録されました",
+    "openclawDefaultModelSet": "デフォルトモデルに設定しました",
+    "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"
   },
   "confirm": {
     "deleteProvider": "プロバイダーを削除",

src/i18n/locales/zh.json

@@ -88,6 +88,8 @@
     "addOpenCodeProvider": "添加 OpenCode 供应商",
     "addToConfig": "添加",
     "removeFromConfig": "移除",
+    "setAsDefault": "启用",
+    "isDefault": "默认",
     "inConfig": "已添加",
     "addProviderHint": "填写信息后即可在列表中快速切换供应商。",
     "editClaudeProvider": "编辑 Claude Code 供应商",
@@ -163,7 +165,10 @@
     "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",
     "openLinkFailed": "链接打开失败",
-    "openclawModelsRegistered": "模型已注册到 /model 列表"
+    "openclawModelsRegistered": "模型已注册到 /model 列表",
+    "openclawDefaultModelSet": "已设为默认模型",
+    "openclawDefaultModelSetFailed": "设置默认模型失败",
+    "openclawNoModels": "该供应商没有配置模型"
   },
   "confirm": {
     "deleteProvider": "删除供应商",