feat(#152): suppression complète grossesse multiple / est_multiple.

Retire le champ partout : BDD (migration + seed), entity/DTO/services Nest,
modèles et payloads Flutter, scripts de test et docs. Back et front alignés
(forbidNonWhitelisted). Aucun fantôme de compat.

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

backend/src/routes/parents/dto/dossier-famille-complet.dto.ts

@@ -54,9 +54,6 @@ export class DossierFamilleEnfantDto {
     description: 'Consentement affichage photo (colonne consentement_photo)',
   })
   consent_photo?: boolean;
-
-  @ApiProperty({ required: false, description: 'Grossesse multiple (est_multiple)' })
-  est_multiple?: boolean;
 }
 
 /** Réponse GET /parents/dossier-famille/:numeroDossier – dossier famille complet. Ticket #119 */

backend/src/routes/parents/parents.service.ts

@@ -370,7 +370,6 @@ export class ParentsService {
       status: child.status,
       photo_url: child.photo_url ?? undefined,
       consent_photo: child.consent_photo,
-      est_multiple: child.is_multiple,
     };
   }