Chore: remove promotional copy and home-training wording

client/src/pages/Login.tsx

@@ -37,13 +37,13 @@ export default function Login() {
             <Target className="w-8 h-8 text-primary" />
           </div>
           <h1 className="text-3xl font-bold tracking-tight">Tennis Hub</h1>
-          <p className="text-muted-foreground mt-2">AI网球训练助手</p>
+          <p className="text-muted-foreground mt-2">训练与分析入口</p>
         </div>
 
         <Card className="border-0 shadow-xl">
           <CardHeader className="text-center pb-2">
-            <CardTitle className="text-xl" data-testid="login-title">开始训练</CardTitle>
-            <CardDescription>输入用户名即可开始使用</CardDescription>
+            <CardTitle className="text-xl" data-testid="login-title">登录</CardTitle>
+            <CardDescription>输入用户名后进入系统</CardDescription>
           </CardHeader>
           <CardContent>
             <form onSubmit={handleLogin} className="space-y-4">
@@ -96,7 +96,7 @@ export default function Login() {
         </Card>
 
         <p className="text-center text-xs text-muted-foreground mt-6">
-          输入用户名即可使用全部功能
+          输入用户名后进入系统
         </p>
       </div>
     </div>