fix: 自助修改密码后断开 VPN 连接并登出所有 Web 会话

- auth.go: ChangePassword 失效所有会话（不再排除当前会话），调用 KickUser 断开 VPN 隧道
- ProfileView.vue: 改密成功后 logout 清除 token，跳转登录页并携带 msg 参数
- LoginView.vue: 读取 query.msg 显示"密码已修改，请重新登录"绿色提示
- zh.ts/en.ts: 新增 login.passwordChanged 国际化 key

frontend/src/locales/en.ts

@@ -45,6 +45,7 @@ export default {
     loginFailed: 'Login failed',
     loggingIn: 'Logging in...',
     loginButton: 'Login',
+    passwordChanged: 'Password changed, please log in again',
   },
   profile: {
     title: 'Profile',

frontend/src/locales/zh.ts

@@ -45,6 +45,7 @@ export default {
     loginFailed: '登录失败',
     loggingIn: '登录中...',
     loginButton: '登录',
+    passwordChanged: '密码已修改，请重新登录',
   },
   profile: {
     title: '用户信息',

frontend/src/views/LoginView.vue

@@ -1,16 +1,18 @@
 <script setup lang="ts">
 import { ref } from 'vue'
-import { useRouter } from 'vue-router'
+import { useRouter, useRoute } from 'vue-router'
 import { useI18n } from 'vue-i18n'
 import { useAuthStore } from '@/stores/auth'
 
 const router = useRouter()
+const route = useRoute()
 const authStore = useAuthStore()
 const { t } = useI18n()
 
 const username = ref('')
 const password = ref('')
 const error = ref('')
+const successMsg = ref(route.query.msg === 'password_changed' ? t('login.passwordChanged') : '')
 const loading = ref(false)
 
 async function handleLogin() {
@@ -71,6 +73,7 @@ async function handleLogin() {
           />
         </div>
         <p v-if="error" class="text-sm text-red-500">{{ error }}</p>
+        <p v-if="successMsg" class="text-sm text-green-500">{{ successMsg }}</p>
         <button
           type="submit"
           :disabled="loading"

frontend/src/views/ProfileView.vue

@@ -1,9 +1,11 @@
 <script setup lang="ts">
 import { onMounted, ref } from 'vue'
+import { useRouter } from 'vue-router'
 import { useI18n } from 'vue-i18n'
 import { useAuthStore } from '@/stores/auth'
 
 const authStore = useAuthStore()
+const router = useRouter()
 const { t } = useI18n()
 
 onMounted(async () => {
@@ -49,6 +51,8 @@ async function handleChangePassword() {
       throw new Error(data.error || t('profile.passwordChangeFailed'))
     }
     showPasswordModal.value = false
+    authStore.logout()
+    router.push({ name: 'login', query: { msg: 'password_changed' } })
   } catch (e: any) {
     passwordError.value = e.message || t('profile.passwordChangeFailed')
   } finally {