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/subscribe-plans/subscribe-plans.js

@@ -11,6 +11,14 @@ Page({
     purchasing: false
   },
 
+  onBack: function () {
+    wx.navigateBack({
+      fail: function () {
+        wx.reLaunch({ url: '/pages/index/index' })
+      }
+    })
+  },
+
   onLoad: function () {
     var app = getApp()
     this.setData({ statusBarHeight: app.globalData.statusBarHeight })

miniprogram/pages/subscribe-plans/subscribe-plans.wxml

@@ -1,5 +1,6 @@
 <view class="page">
   <view class="page-header page-header-gold" style="padding-top: {{statusBarHeight + 24}}px;">
+    <view class="nav-back" bindtap="onBack">‹ 返回</view>
     <view class="page-header-title">订阅服务</view>
     <view class="page-header-subtitle">解锁智能模式</view>
   </view>