Add 卓米会 mini program and admin server.

Initial commit of the WeChat mini program, Express backend, and admin console.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/lib/wechat.js

@@ -0,0 +1,34 @@
+const crypto = require('crypto')
+const { HttpError } = require('./http')
+
+async function code2session(code, deviceId) {
+  const appid = process.env.WX_APPID
+  const secret = process.env.WX_SECRET
+  if (!appid || !secret) {
+    const seed = deviceId || 'guest'
+    return {
+      openid: `demo_${crypto.createHash('sha1').update(seed).digest('hex').slice(0, 16)}`,
+      demo: true
+    }
+  }
+
+  const url = new URL('https://api.weixin.qq.com/sns/jscode2session')
+  url.search = new URLSearchParams({
+    appid,
+    secret,
+    js_code: code,
+    grant_type: 'authorization_code'
+  }).toString()
+
+  let session
+  try {
+    const res = await fetch(url, { signal: AbortSignal.timeout(8000) })
+    session = await res.json()
+  } catch (error) {
+    throw new HttpError(502, '微信登录服务不可用')
+  }
+  if (!session.openid) throw new HttpError(400, session.errmsg || '微信登录失败')
+  return { openid: session.openid, demo: false }
+}
+
+module.exports = { code2session }