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/config/env.js

@@ -7,7 +7,10 @@ var API_BASES = {
   prod: 'https://replace-with-scf-prod-url' // TODO: replace with actual production SCF URL
 }
 
+var __DEV__ = ENV !== 'prod'
+
 module.exports = {
   ENV: ENV,
-  API_BASE: API_BASES[ENV]
+  API_BASE: API_BASES[ENV],
+  __DEV__: __DEV__
 }