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/admin/index.js

@@ -0,0 +1,23 @@
+const cloud = require('wx-server-sdk')
+cloud.init({ env: cloud.DYNAMIC_CURRENT_ENV })
+const db = cloud.database()
+
+exports.main = async (event, context) => {
+  const { action } = event
+
+  if (action === 'dashboard') {
+    const deviceCount = await db.collection('bindings').where({ status: 'active' }).count()
+    const userCount = await db.collection('users').count()
+    const treatmentCount = await db.collection('treatment_records').count()
+    return {
+      code: 0,
+      data: {
+        device_count: deviceCount.total,
+        user_count: userCount.total,
+        treatment_count: treatmentCount.total
+      }
+    }
+  }
+
+  return { code: -1, message: '未知操作' }
+}

miniprogram/cloud-functions/admin/package.json

@@ -0,0 +1,9 @@
+{
+  "name": "admin",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "dependencies": {
+    "wx-server-sdk": "~2.6.3"
+  }
+}