fix: login page uses email only since username is auto-generated

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/views/Login.vue

@@ -15,7 +15,7 @@ const loading = ref(false)
 
 async function handleLogin() {
   if (!identity.value || !password.value) {
-    ElMessage.warning('请输入用户名/邮箱和密码')
+    ElMessage.warning('请输入邮箱和密码')
     return
   }
 
@@ -45,11 +45,12 @@ async function handleLogin() {
 
       <form class="login-form" @submit.prevent="handleLogin">
         <div class="form-group">
-          <label for="identity">用户名 / 邮箱</label>
+          <label for="identity">邮箱</label>
           <el-input
             id="identity"
             v-model="identity"
-            placeholder="请输入用户名或邮箱"
+            type="email"
+            placeholder="请输入注册时的邮箱"
             required
           />
         </div>