fix: 绑定页面登录态检查 + 登录后返回原页面

Login.vue:
- goCasdoorLogin() 前将 redirect 参数存入 sessionStorage
- 登录成功后检查 sessionStorage 跳回原页面
- wecomLogin 流程同样支持 returnUrl

WecomBind.vue:
- onMounted 检测未登录 → 跳转 /login?redirect=/wecom-bind?token=xxx
- 登录后自动回到绑定页面，auth.user 不再为空

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

frontend/src/views/Login.vue

@@ -18,6 +18,8 @@ onMounted(async () => {
     loading.value = true
     try {
       await auth.casdoorLogin(code, state)
+      const returnUrl = sessionStorage.getItem('login_return_url')
+      if (returnUrl) { sessionStorage.removeItem('login_return_url'); router.push(returnUrl); return }
       ElMessage.success('登录成功')
       router.push(auth.isManager ? '/m' : '/')
     } catch (e: any) {
@@ -45,6 +47,8 @@ onMounted(async () => {
         name: res.data.name,
         role: res.data.role,
       })
+      const returnUrl = sessionStorage.getItem('login_return_url')
+      if (returnUrl) { sessionStorage.removeItem('login_return_url'); router.push(returnUrl); return }
       ElMessage.success('登录成功')
       router.push(auth.isManager ? '/m' : '/')
     } catch (e: any) {
@@ -56,7 +60,11 @@ onMounted(async () => {
 })
 
 function goCasdoorLogin() {
-  // Redirect to Casdoor authorization page
+  // Save return URL before redirecting to Casdoor
+  const returnUrl = (route.query.redirect as string) || ''
+  if (returnUrl) {
+    sessionStorage.setItem('login_return_url', returnUrl)
+  }
   const endpoint = import.meta.env.VITE_CASDOOR_ENDPOINT
   const clientId = import.meta.env.VITE_CASDOOR_CLIENT_ID
   const redirectUri = encodeURIComponent(window.location.origin + '/login')

frontend/src/views/WecomBind.vue

@@ -18,6 +18,12 @@ onMounted(() => {
   if (!bindToken) {
     errorMsg.value = '无效的绑定链接'
     setTimeout(() => router.replace('/'), 2000)
+    return
+  }
+  if (!auth.isLoggedIn) {
+    // Not logged in yet — redirect to login, then come back here
+    router.push(`/login?redirect=${encodeURIComponent(route.fullPath)}`)
+    return
   }
 })