fix: back button alignment, mock bind flow, and timezone bug

- nav-back: add text-align:left to override page-header's center
- ble-connect mock: call bind API first to get fresh token before
  confirm, instead of relying on potentially stale URL params
- utils.js: use local time instead of UTC for toMysqlDate, fixing
  timezone mismatch with MySQL NOW() that caused bind tokens to
  appear immediately expired

miniprogram/app.wxss

@@ -244,6 +244,7 @@ page {
   color: rgba(255, 255, 255, 0.85);
   padding: 8rpx 0;
   margin-bottom: 8rpx;
+  text-align: left;
 }
 
 .nav-back-light {