No address step before signing in when there's only one mail server

The server's own page asks for the username, so with a single server the
sign-in page keeps only the own-device choice. With several servers the
address still comes first, since its domain picks the server. One new string,
in all nine catalogues.

web/src/locales/zh-Hans.ts

@@ -1223,6 +1223,7 @@ export const catalog: Catalog = {
     "Could not send the receipt: {error}": "无法发送已读回执：{error}",
     "Could not sign in.": "无法登录。",
     "You'll enter your password on your mail server's sign-in page.": "您将在邮件服务器的登录页面上输入密码。",
+    "You'll sign in on your mail server's own page.": "您将在邮件服务器自己的页面上登录。",
     "This sign-in didn't start in this browser. Try again.": "此次登录不是在这个浏览器中发起的。请重试。",
     "The sign-in took too long. Try again.": "登录耗时过长。请重试。",
     "Sign-in was cancelled.": "登录已取消。",