refactor: migrate to WeChat cloud development

- 新增 cloud-functions/ 目录（6个云函数：auth/device/subscription/treatment/user/admin）
- 云函数使用 wx-server-sdk + 云数据库（不再依赖 MySQL）
- auth 云函数通过 cloud.getWXContext() 自动获取 openid，无需手动 wx.login
- request.js 改为通过 wx.cloud.callFunction() 调用云函数
- 登录流程简化：点击授权 → 直接调 auth 云函数 → 获取用户信息
- 保留 HTTP 模式切换能力（USE_CLOUD 变量控制）

miniprogram/cloud-functions/user/index.js

@@ -0,0 +1,39 @@
+const cloud = require('wx-server-sdk')
+cloud.init({ env: cloud.DYNAMIC_CURRENT_ENV })
+const db = cloud.database()
+
+exports.main = async (event, context) => {
+  const wxContext = cloud.getWXContext()
+  const openid = wxContext.OPENID
+  const { action } = event
+
+  if (action === 'profile') {
+    const users = await db.collection('users').where({ openid }).get()
+    if (users.data.length === 0) return { code: 1001, message: '用户不存在' }
+    const user = users.data[0]
+    const binds = await db.collection('bindings').where({ openid, status: 'active' }).count()
+    return {
+      code: 0,
+      data: {
+        user_id: user._id,
+        nickname: user.nickname || '用户' + openid.slice(-4),
+        avatar_url: user.avatar_url || '',
+        phone: user.phone || '',
+        gender: user.gender || 0,
+        device_count: binds.total,
+        created_at: user.created_at
+      }
+    }
+  }
+
+  if (action === 'update') {
+    const updates = {}
+    if (event.data.nickname) updates.nickname = event.data.nickname
+    if (event.data.avatar_url) updates.avatar_url = event.data.avatar_url
+    if (event.data.gender !== undefined) updates.gender = event.data.gender
+    await db.collection('users').where({ openid }).update({ data: updates })
+    return { code: 0, data: {} }
+  }
+
+  return { code: -1, message: '未知操作' }
+}