feat(auth): 服务端托管 Google OAuth，desktop 轮询登录；补充服务端环境变量文档

apps/desktop/dist/main.js

@@ -510,6 +510,7 @@ async function doDemoLogin() {
   if (!invoke) return;
   setLoginError("");
   loginButton.disabled = true;
+  loginButton.textContent = "正在打开浏览器...";
   try {
     let data = await invoke("continue_demo_login");
     data = await ensureUnlockedShell(data);
@@ -518,6 +519,7 @@ async function doDemoLogin() {
   } catch (error) {
     setLoginError(String(error));
   } finally {
+    loginButton.textContent = "前往浏览器登录";
     loginButton.disabled = false;
   }
 }