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

admin-console/src/views/UserDetailView.vue

@@ -5,7 +5,6 @@
     <view class="page-card" v-if="user">
       <view class="page-header">
         <text class="page-title">👥 用户详情 - {{ user.nickname || user.user_id }}</text>
-        <button class="btn-primary btn-sm">发送通知</button>
       </view>
 
       <view class="user-profile">