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/App.tsx

@@ -1,7 +1,6 @@
 import type { ReactNode } from "react";
 import { NavLink, Navigate, Route, Routes } from "react-router-dom";
 import { clearSession, getToken, getUsername } from "./api/client";
-import InstallBadge from "./components/InstallBadge";
 import LoginPage from "./pages/Login";
 import PlanPage from "./pages/Plan";
 import TradesPage from "./pages/Trades";
@@ -14,8 +13,16 @@ function Shell({ children }: { children: ReactNode }) {
     <div className="app-shell">
       <header className="topnav">
         <div className="topnav-side left">
-          <div className="brand">比特骆驼自动化对冲系统</div>
-          <InstallBadge />
+          <div className="brand">
+            <img
+              className="brand-mark"
+              src="/icons/brand.png"
+              alt=""
+              width={28}
+              height={28}
+            />
+            <span>比特骆驼自动化对冲系统</span>
+          </div>
         </div>
         <nav className="topnav-center">
           <NavLink to="/plan" className={({ isActive }) => (isActive ? "active" : "")}>