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/login/login.wxml

@@ -18,10 +18,10 @@
     </button>
 
     <!-- 手机号授权已预留。需要时展示该按钮并隐藏上面的普通登录按钮。 -->
-    <button class="phone-btn disabled-phone-btn" open-type="getPhoneNumber" bindgetphonenumber="onGetPhoneNumber" disabled="{{loading}}">
+    <button wx:if="{{false}}" class="phone-btn disabled-phone-btn" open-type="getPhoneNumber" bindgetphonenumber="onGetPhoneNumber" disabled="{{loading}}">
       授权手机号登录（预留）
     </button>
 
-    <view class="agreement">登录即表示同意《用户协议》和《隐私政策》</view>
+    <view class="agreement" bindtap="onAgreement">登录即表示同意《用户协议》和《隐私政策》</view>
   </view>
 </view>