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

miniprogram/pages/wear-check/wear-check.wxml

@@ -11,9 +11,10 @@
       <view class="device-row-info">
         <view class="device-row-name">
           光子美容仪
-          <text class="status-badge status-badge-green">已连接</text>
+          <text class="status-badge status-badge-green" wx:if="{{connected}}">已连接</text>
+          <text class="status-badge" style="background:#ccc;" wx:else>未连接</text>
         </view>
-        <view class="device-row-battery">电量 85%</view>
+        <view class="device-row-battery">电量 {{battery}}%</view>
       </view>
     </view>