feat: use login(userId, userSig) with demo API pre-fetch

pages/login/login.js

@@ -35,7 +35,23 @@ Page({
     this.setData({ loading: true, error: '' })
     try {
       const sdk = app.globalData.sdk
-      await sdk.loginWithDemo(userId, password)
+      const config = sdk.requireConfig()
+      // 1. Call demo API to get userSig
+      const res = await new Promise((resolve, reject) => {
+        wx.request({
+          url: `${config.apiUrl}/api/demo/auth/login`,
+          method: 'POST',
+          header: { 'Content-Type': 'application/json' },
+          data: { appId: config.appKey, userId, password },
+          success: (r) => resolve(r.data),
+          fail: (err) => reject(err),
+        })
+      })
+      if (res.code !== 200) {
+        throw new Error(res.message || '登录失败')
+      }
+      // 2. Login with userSig
+      await sdk.login(userId, res.data.imToken)
       app.globalData.userId = userId
       wx.navigateTo({ url: '/pages/chat/chat' })
     } catch (err) {