feat: complete feature gaps across all modules

Server:
- Add settings-cache with 60s TTL for feature toggle checks
- Enforce maintenance_mode on login, enable_binding on device bind

Admin console:
- Remove dead "发送通知" button from user detail
- Firmware check calls real API and compares versions

Miniprogram:
- Wear-check: dynamic battery/connected from BLE state
- Login: hide non-functional phone auth button
- Treating: show actual selected regions instead of hardcoded "全脸"
- Index: display subscription status with tap to manage
- Auto-scan: show "待检测" instead of "--" for PD data
- Agreements: tap shows "内容建设中" modal

server/src/routes/device.js

@@ -2,6 +2,7 @@ const router = require('express').Router()
 const { ok, fail } = require('../lib/response')
 const { requireUser } = require('../middleware/auth')
 const { randomHex } = require('../lib/auth')
+const { getSettings } = require('../lib/settings-cache')
 const bindingDao = require('../dao/binding.dao')
 const deviceDao = require('../dao/device.dao')
 const commandDao = require('../dao/command.dao')
@@ -12,6 +13,9 @@ const logDao = require('../dao/log.dao')
 const wrap = fn => (req, res, next) => fn(req, res, next).catch(next)
 
 router.post('/device/bind', requireUser, wrap(async (req, res) => {
+  const settings = await getSettings()
+  if (settings.enable_binding === false) return res.json(fail(2001, '设备绑定已关闭'))
+
   const deviceId = String(req.body.device_id || '').trim()
   if (!deviceId) return res.json(fail(2001, 'device_id required'))