Add PWA install badge for desktop and tablet (manifest, SW, Add to Home Screen).

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/pages/Login.tsx

@@ -1,6 +1,7 @@
 import { FormEvent, useState } from "react";
 import { useNavigate } from "react-router-dom";
 import { login, setSession } from "../api/client";
+import InstallBadge from "../components/InstallBadge";
 
 export default function LoginPage() {
   const nav = useNavigate();
@@ -27,8 +28,11 @@ export default function LoginPage() {
   return (
     <div className="login-wrap">
       <form className="login-box" onSubmit={onSubmit}>
-        <h1>OKX 自动化对冲系统</h1>
-        <p>模拟盘登录</p>
+        <div className="login-title-row">
+          <h1>OKX 自动化对冲系统</h1>
+          <InstallBadge />
+        </div>
+        <p>模拟盘登录 · 支持电脑/平板安装为应用</p>
         {err ? <div className="err">{err}</div> : null}
         <div className="field">
           <label htmlFor="user">用户名</label>