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 {

miniprogram/pages/ble-connect/ble-connect.js

@@ -96,38 +96,35 @@ Page({
     this.startBleConnect()
   },
 
-  onMockConnect: function () {
+  _mockConfirmBind: function () {
     var self = this
-    clearTimeout(this._scanTimer)
-    ble.stopScan()
     self.setData({ state: 'binding' })
-    // Skip BLE bind, confirm directly with server
-    http.post('/api/v1/device/bind/confirm', {
-      device_id: self.data.deviceId,
-      bind_token: self.data.bindToken
+    http.post('/api/v1/device/bind', {
+      device_id: self.data.deviceId
+    }).then(function (data) {
+      return http.post('/api/v1/device/bind/confirm', {
+        device_id: data.device_id,
+        bind_token: data.bind_token
+      })
     }).then(function () {
       self.setData({ state: 'done' })
       wx.redirectTo({
         url: '/pages/bind-success/bind-success?device_id=' + self.data.deviceId
       })
     }).catch(function (err) {
-      self.setData({ state: 'error', error: err.message || '模拟确认失败' })
+      self.setData({ state: 'error', error: err.message || '模拟绑定失败' })
     })
   },
 
-  onMockBindSuccess: function () {
-    var self = this
+  onMockConnect: function () {
     clearTimeout(this._scanTimer)
     ble.stopScan()
-    http.post('/api/v1/device/bind/confirm', {
-      device_id: self.data.deviceId,
-      bind_token: self.data.bindToken
-    }).then(function () {
-      wx.redirectTo({
-        url: '/pages/bind-success/bind-success?device_id=' + self.data.deviceId
-      })
-    }).catch(function (err) {
-      self.setData({ state: 'error', error: err.message || '模拟确认失败' })
-    })
+    this._mockConfirmBind()
+  },
+
+  onMockBindSuccess: function () {
+    clearTimeout(this._scanTimer)
+    ble.stopScan()
+    this._mockConfirmBind()
   }
 })