fix: address critical security and data integrity issues from cross-audit

- Add expire_time > NOW() filter to findActive() preventing stale subscriptions
- Add express-rate-limit on login endpoints (user: 10/15min, admin: 5/15min)
- Add production guard for default admin credentials
- Fix BLE bindDevice userId encoding (uint32 instead of hexToBytes on numeric)
- Wrap adminCreate in transaction to prevent race condition
- Add settings cache invalidation after admin saves
- Read trial_days from settings instead of hardcoding 7
- Fix double JSON.stringify in commandDao.finish call
- Cancel stale pending bindings before creating new ones
- Reduce token refresh grace period from 3 days to 1 day
- Fix subscribe-success to fetch expiry from server (correct for renewals)
- Add keep-alive name property to DashboardView and SettingsView
- Fix BLE disconnect() to preserve listener registrations across reconnects

miniprogram/services/ble/connection.js

@@ -236,7 +236,9 @@ function disconnect() {
   _chars = {}
   var commands = require('./commands')
   commands.clearPendingAcks()
-  _listeners = {}
+  // Only emit disconnected event; do not clear _listeners so that
+  // subscribers (other modules) retain their registrations across reconnects.
+  emit('disconnect_cleanup', null)
   wx.closeBluetoothAdapter({})
 }