feat: add first-run confirmation dialog for stream check

Show an informational dialog when users first click the health check
button, explaining its limitations (OAuth providers, relay services,
Bedrock). The dialog persists the confirmation in settings so it only
appears once per device.

src/types.ts

@@ -219,6 +219,8 @@ export interface Settings {
   proxyConfirmed?: boolean;
   // User has confirmed the usage query first-run notice
   usageConfirmed?: boolean;
+  // User has confirmed the stream check first-run notice
+  streamCheckConfirmed?: boolean;
   // 首选语言（可选，默认中文）
   language?: "en" | "zh" | "ja";