feat: support JW_ device ID format in QR scan and BLE matching

- parseDeviceId accepts hex with spaces (e.g. "672B6D5A 4DCD861")
- BLE scan does exact match on "JW_<device_id>" when target is known
- Manual input placeholder updated to show new format

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

@@ -52,6 +52,7 @@ Page({
     }, SCAN_TIMEOUT)
 
     ble.startScan({
+      targetDeviceId: self.data.deviceId,
       onFound: function (device) {
         clearTimeout(self._scanTimer)
         self.setData({ state: 'connecting' })