fix: improve UX and fix admin console display issues

Miniprogram:
- Add back buttons to all custom-nav pages
- Add debug/mock buttons (BLE connect, wear check, treatment)
  controlled by __DEV__ flag (hidden in prod)

Admin console:
- Fix log page using nonexistent fields (operator_type, target_type)
  now correctly reads admin_id/user_id/action/detail from API
- Fix subscription date fields (started_at→start_time, expired_at→expire_time)
- Wire up subscription detail/extend/renew action buttons
- Wire up device detail "查看完整日志" button
- Add "创建订阅" button to subscription toolbar
- Fix subscription status mapping (2=expired, 3=cancelled)

Docs:
- Add detailed architecture docs for server, miniprogram, admin console

miniprogram/pages/auto-scan/auto-scan.wxml

@@ -1,5 +1,6 @@
 <view class="page">
   <view class="page-header page-header-pink" style="padding-top: {{statusBarHeight + 24}}px;">
+    <view class="nav-back" bindtap="onBack">‹ 返回</view>
     <view class="page-header-title">自动扫描</view>
     <view class="page-header-subtitle">正在识别面部...</view>
   </view>
@@ -15,6 +16,11 @@
 
     <view class="scan-hint">请将面罩对准面部</view>
 
+    <view class="debug-actions" wx:if="{{devMode}}">
+      <view class="debug-label">🔧 调试工具</view>
+      <button class="btn-secondary btn-sm" bindtap="onMockScanDone">模拟扫描完成</button>
+    </view>
+
     <view class="scan-progress" wx:if="{{scanning}}">
       正在扫描... <text class="highlight">{{regionData.length || 3}}</text> 个区域
     </view>