fix(#194): insert card_responses avec id_card explicite

TypeORM nullifiait id_card (conflit Column/JoinColumn) → 500 sur respond.

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

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

@@ -204,14 +204,12 @@ export class CardsService {
       throw new BadRequestException('Motivation obligatoire en cas de refus');
     }
 
-    await this.responsesRepo.save(
+    await this.responsesRepo.insert({
-      this.responsesRepo.create({
       id_card: card.id,
       id_utilisateur: userId,
       action: dto.action,
-        comment: dto.comment?.trim(),
+      comment: dto.comment?.trim() || null,
-      }),
+    });
-    );
 
     if (card.id_absence) {
       if (dto.action === CardResponseActionType.ACCEPT || dto.action === CardResponseActionType.ACK) {