fix: preserve resolved flag when closing tickets

frontend/src/features/tickets/TicketDetailPage.tsx

@@ -90,7 +90,7 @@ export function TicketDetailPage({ ticketId }: { ticketId: number }) {
     values: {
       remark: string
       resolution: string
-      is_resolved: boolean
+      is_resolved?: boolean
       replied_to_customer: boolean
     }
   ) {

frontend/src/features/tickets/TicketTransitionDialog.tsx

@@ -32,7 +32,7 @@ type TicketTransitionDialogProps = {
     values: {
       remark: string
       resolution: string
-      is_resolved: boolean
+      is_resolved?: boolean
       replied_to_customer: boolean
     }
   ) => Promise<void>
@@ -70,7 +70,7 @@ export function TicketTransitionDialog({
       await onSubmit(status, {
         remark: remark.trim(),
         resolution: resolution.trim(),
-        is_resolved: status === 'resolved',
+        is_resolved: status === 'resolved' ? true : undefined,
         replied_to_customer: repliedToCustomer
       })
       onOpenChange(false)