feat: 企微绑定入口 — BindWechat.vue + 路由

新增 /bind-wechat 公开路由:
- 页面加载后自动重定向到企微 OAuth 授权页
- scope=snsapi_base (静默授权，无需用户确认)
- 回调到 /login?wecom_code=xxx → 自动绑定

用法: 企微工作台应用主页设为 https://qj.dhdx.fun/bind-wechat

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

frontend/src/router/index.ts

@@ -16,6 +16,12 @@ const router = createRouter({
       component: () => import('@/views/BindWecom.vue'),
       meta: { public: true },
     },
+    {
+      path: '/bind-wechat',
+      name: 'BindWechat',
+      component: () => import('@/views/BindWechat.vue'),
+      meta: { public: true },
+    },
     // Mobile routes (manager-facing)
     {
       path: '/m',