fix(cards): FK card_responses via relation JoinColumn + save(create)

Double mapping @Column/@JoinColumn sur id_card ; persist response via
card/user relations. Garde update() sur l’instance (évite save parent
qui nullifiait les FK enfants).

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/modules/cards/cards.service.spec.ts

@@ -24,6 +24,7 @@ describe('CardsService (#194)', () => {
   const cardsRepo = {
     create: jest.fn((x) => x),
     save: jest.fn(async (x) => ({ ...x, id: x.id ?? 'card-1', cree_le: new Date(), modifie_le: new Date() })),
+    update: jest.fn(async () => ({ affected: 1 })),
     findOne: jest.fn(),
     delete: jest.fn(),
     createQueryBuilder: jest.fn(),
@@ -37,7 +38,8 @@ describe('CardsService (#194)', () => {
   };
   const responsesRepo = {
     create: jest.fn((x) => x),
-    save: jest.fn(),
+    save: jest.fn(async (x) => x),
+    insert: jest.fn(),
   };
   const amChildrenRepo = { findOne: jest.fn() };
   const parentsChildrenRepo = { find: jest.fn(), findOne: jest.fn() };
@@ -226,4 +228,57 @@ describe('CardsService (#194)', () => {
     expect(ids).toEqual(['am-1', 'p-1', 'p-2']);
     expect(saved.find((m) => m.id_utilisateur === 'p-2')?.is_creator).toBe(false);
   });
+
+  it('parent accepte conge_am → response via relation + carte traitee', async () => {
+    cardsRepo.findOne.mockResolvedValue({
+      id: 'card-1',
+      type_code: 'conge_am',
+      id_placement: 'pl-1',
+      id_evenement: 'ev-1',
+      cree_par: 'am-1',
+      operation: CardOperationType.CREATE,
+      statut: CardInstanceStatutType.OUVERTE,
+      payload: { date_debut: '2026-10-27', date_fin: '2026-10-31' },
+      purge_at: new Date(),
+      cree_le: new Date(),
+      modifie_le: new Date(),
+      type: {
+        titre: 'Congé AM',
+        response_mode: CardResponseModeType.ACCEPT_REFUSE,
+        retention_days: 14,
+      },
+      responses: [],
+      audience: [
+        { id_utilisateur: 'am-1' },
+        { id_utilisateur: 'p-1' },
+        { id_utilisateur: 'p-2' },
+      ],
+    });
+    audienceRepo.findOne.mockResolvedValue({ id_card: 'card-1', id_utilisateur: 'p-1' });
+    evenementsService.maj.mockResolvedValue({});
+
+    const res = await service.repondre('p-1', RoleType.PARENT, 'card-1', {
+      action: 'accept' as never,
+    });
+
+    expect(responsesRepo.create).toHaveBeenCalledWith(
+      expect.objectContaining({
+        card: { id: 'card-1' },
+        user: { id: 'p-1' },
+        action: 'accept',
+      }),
+    );
+    expect(responsesRepo.save).toHaveBeenCalled();
+    expect(evenementsService.maj).toHaveBeenCalledWith(
+      'p-1',
+      RoleType.PARENT,
+      'ev-1',
+      expect.objectContaining({ statut: StatutEvenementAgendaType.ACCEPTE }),
+    );
+    expect(cardsRepo.update).toHaveBeenCalledWith(
+      { id: 'card-1' },
+      expect.objectContaining({ statut: CardInstanceStatutType.TRAITEE }),
+    );
+    expect(res.statut).toBe(CardInstanceStatutType.TRAITEE);
+  });
 });