Link existing guest to booking by phone

src/main/kotlin/com/android/trisolarisserver/controller/Guests.kt

@@ -55,7 +55,10 @@ class Guests(
         }
         val existing = guestRepo.findByPropertyIdAndPhoneE164(propertyId, phone)
         if (existing != null) {
-            throw ResponseStatusException(HttpStatus.CONFLICT, "Guest already exists")
+            booking.primaryGuest = existing
+            booking.updatedAt = OffsetDateTime.now()
+            bookingRepo.save(booking)
+            return setOf(existing).toResponse(guestVehicleRepo, guestRatingRepo).first()
         }
 
         val now = OffsetDateTime.now()