Add confirm password field on registration

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/LoginModal.vue

@@ -29,6 +29,14 @@
           class="login-input"
           @keydown.enter="submit"
         />
+        <input
+          v-if="mode === 'register'"
+          v-model="confirmPassword"
+          type="password"
+          placeholder="确认密码"
+          class="login-input"
+          @keydown.enter="submit"
+        />
         <input
           v-if="mode === 'register'"
           v-model="displayName"
@@ -61,6 +69,7 @@ const ui = useUiStore()
 const mode = ref('login')
 const username = ref('')
 const password = ref('')
+const confirmPassword = ref('')
 const displayName = ref('')
 const errorMsg = ref('')
 const loading = ref(false)
@@ -76,6 +85,10 @@ async function submit() {
     errorMsg.value = '请输入密码'
     return
   }
+  if (mode.value === 'register' && password.value !== confirmPassword.value) {
+    errorMsg.value = '两次输入的密码不一致'
+    return
+  }
 
   loading.value = true
   try {