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/treatment/index.js

@@ -0,0 +1,42 @@
+const cloud = require('wx-server-sdk')
+cloud.init({ env: cloud.DYNAMIC_CURRENT_ENV })
+const db = cloud.database()
+const _ = db.command
+
+exports.main = async (event, context) => {
+  const wxContext = cloud.getWXContext()
+  const openid = wxContext.OPENID
+  const { action } = event
+
+  if (action === 'sync') {
+    const d = event.data
+    await db.collection('treatment_records').add({
+      data: {
+        openid,
+        session_id: d.session_id || 'S' + Date.now(),
+        device_id: d.device_id || '',
+        regions: d.regions || 0,
+        total_duration_ms: d.total_duration_ms || 0,
+        mode: d.mode || 0,
+        avg_pd: d.avg_pd || 0,
+        created_at: db.serverDate()
+      }
+    })
+    return { code: 0, data: { session_id: d.session_id || 'S' + Date.now() } }
+  }
+
+  if (action === 'history') {
+    const { page = 1, page_size = 20 } = event.data || {}
+    const totalRes = await db.collection('treatment_records').where({ openid }).count()
+    const records = await db.collection('treatment_records')
+      .where({ openid })
+      .orderBy('created_at', 'desc')
+      .skip((page - 1) * page_size)
+      .limit(page_size)
+      .get()
+
+    return { code: 0, data: { records: records.data, total: totalRes.total } }
+  }
+
+  return { code: -1, message: '未知操作' }
+}