fix: 设备未绑定短编号时反向查找缓存抛 NoSuchElementException，改为 orElse(null)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

car-wash-service/src/main/java/com/kym/service/cache/KymCache.java

@@ -215,7 +215,7 @@ public enum KymCache {
      * 通过productKey和deviceName获取设备短编号
      */
     public String getShortIdByProductKeyAndDeviceName(String productKey, String deviceName) {
-        return SHORT_ID_TO_PRODUCT_KEY_AND_DEVICE_NAME_MAPPING.entrySet().stream().filter(entry -> (productKey + "," + deviceName).equals(entry.getValue())).map(Map.Entry::getKey).findFirst().get();
+        return SHORT_ID_TO_PRODUCT_KEY_AND_DEVICE_NAME_MAPPING.entrySet().stream().filter(entry -> (productKey + "," + deviceName).equals(entry.getValue())).map(Map.Entry::getKey).findFirst().orElse(null);
     }
 
     public void setParkingCouponCode(String code, String parkingCouponUrl, Long seconds) {