Use 比特骆驼 logo for PWA/brand marks, remove install button, docs Ubuntu 22.04 only.

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

frontend/src/pages/Login.tsx

@@ -1,7 +1,6 @@
 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();
@@ -29,8 +28,14 @@ export default function LoginPage() {
     <div className="login-wrap">
       <form className="login-box" onSubmit={onSubmit}>
         <div className="login-title-row">
+          <img
+            className="login-brand-mark"
+            src="/icons/brand.png"
+            alt="比特骆驼"
+            width={48}
+            height={48}
+          />
           <h1>比特骆驼自动化对冲系统</h1>
-          <InstallBadge />
         </div>
         {err ? <div className="err">{err}</div> : null}
         <div className="field">