feat: add provider-specific terminal button

Add a terminal button next to each provider card that opens a new terminal
window with that provider's specific API configuration. This allows using
different providers independently without changing the global setting.

Changes:
- Backend: Add `open_provider_terminal` command that extracts provider
  config and creates a temporary claude settings file
- Frontend: Add terminal button to provider cards with proper callback
  propagation through component hierarchy
- Support macOS (Terminal.app), Linux (gnome-terminal, konsole, etc.),
  and Windows (cmd)

Each provider gets a unique config file named `claude_<providerId>_<pid>.json`
in the temp directory, containing the provider's API configuration.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/lib/api/providers.ts

@@ -61,4 +61,13 @@ export const providersApi = {
       handler(payload);
     });
   },
+
+  /**
+   * 打开指定提供商的终端
+   * 任何提供商都可以打开终端，不受是否为当前激活提供商的限制
+   * 终端会使用该提供商特定的 API 配置，不影响全局设置
+   */
+  async openTerminal(providerId: string, appId: AppId): Promise<boolean> {
+    return await invoke("open_provider_terminal", { providerId, app: appId });
+  },
 };