feat: add bank question via modal + dirty modal guard

- Add question in question bank now opens a modal instead of navigating
  to a full-page form, consistent with the edit modal pattern
- Modal closes are blocked by static backdrop once the user has made any
  change (input, checkbox, drag-reorder, sort, randomize, remove answer)
- Dirty state resets when the modal is fully hidden

src/Controller/Backoffice/QuestionBankController.php

@@ -88,6 +88,8 @@ class QuestionBankController extends AbstractController
     {
         $bankQuestion = new BankQuestion();
 
+        $isModalRequest = $request->headers->has('X-Modal-Request');
+
         $form = $this->createForm(BankQuestionFormType::class, $bankQuestion, ['season' => $season]);
         $form->handleRequest($request);
 
@@ -99,14 +101,29 @@ class QuestionBankController extends AbstractController
 
             $this->addFlash(FlashType::Success, $this->translator->trans('Question added to the question bank'));
 
+            if ($isModalRequest) {
+                return new Response('', Response::HTTP_NO_CONTENT);
+            }
+
             return $this->redirectToRoute('tvdt_backoffice_question_bank', ['seasonCode' => $season->seasonCode]);
         }
 
-        return $this->render('backoffice/question_bank/form.html.twig', [
+        $template = $isModalRequest
+            ? 'backoffice/question_bank/_form_body.html.twig'
+            : 'backoffice/question_bank/form.html.twig';
+
+        $response = $this->render($template, [
             'season' => $season,
             'form' => $form,
             'bankQuestion' => null,
+            'isModal' => $isModalRequest,
         ]);
+
+        if ($form->isSubmitted()) {
+            $response->setStatusCode(Response::HTTP_UNPROCESSABLE_ENTITY);
+        }
+
+        return $response;
     }
 
     #[IsGranted(SeasonVoter::EDIT, subject: 'season')]