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/treating/treating.wxml

@@ -16,7 +16,7 @@
     </view>
 
     <view class="mode-tag-area">
-      <text class="mode-tag">{{mode === 1 ? '✨ 智能模式' : '🔄 普通模式'}} · 全脸护理</text>
+      <text class="mode-tag">{{mode === 1 ? '✨ 智能模式' : '🔄 普通模式'}} · {{regionText}}</text>
     </view>
 
     <view class="relax-card">