Fix lazy-loading in booking balance endpoint

src/main/kotlin/com/android/trisolarisserver/controller/booking/BookingBalances.kt

@@ -11,6 +11,7 @@ import com.android.trisolarisserver.repo.room.RoomStayRepo
 import com.android.trisolarisserver.security.MyPrincipal
 import org.springframework.http.HttpStatus
 import org.springframework.security.core.annotation.AuthenticationPrincipal
+import org.springframework.transaction.annotation.Transactional
 import org.springframework.web.bind.annotation.GetMapping
 import org.springframework.web.bind.annotation.PathVariable
 import org.springframework.web.bind.annotation.RequestMapping
@@ -29,6 +30,7 @@ class BookingBalances(
 ) {
 
     @GetMapping
+    @Transactional(readOnly = true)
     fun getBalance(
         @PathVariable propertyId: UUID,
         @PathVariable bookingId: UUID,