feat: Intégration du backend NestJS depuis YNOV

- Framework: NestJS avec TypeORM
- Authentification: JWT (access + refresh tokens)
- Gestion utilisateurs: CRUD complet avec validation
- Routes: auth, users, parents, assistantes maternelles
- Dockerfile pour conteneurisation

backend/src/entities/children.entity.ts

@@ -0,0 +1,74 @@
+import {
+  Entity, PrimaryGeneratedColumn, Column,
+  OneToMany, ManyToMany, CreateDateColumn, JoinTable
+} from 'typeorm';
+import { Parents } from './parents.entity';
+import { ParentsChildren } from './parents_children.entity';
+import { Dossier } from './dossiers.entity';
+
+export enum StatutEnfantType {
+  A_NAITRE = 'a_naitre',
+  ACTIF = 'actif',
+  SCOLARISE = 'scolarise',
+}
+
+export enum GenreType {
+  H = 'H',
+  F = 'F',
+  AUTRE = 'Autre',
+}
+
+@Entity('enfants')
+export class Children {
+  @PrimaryGeneratedColumn('uuid')
+  id: string;
+
+  @Column({
+    type: 'enum',
+    enum: StatutEnfantType,
+    enumName: 'statut_enfant_type',
+    name: 'statut'
+  })
+  status: StatutEnfantType;
+
+  @Column({ name: 'prenom', length: 100, nullable: true })
+  first_name?: string;
+
+  @Column({ name: 'nom', length: 100, nullable: true })
+  last_name?: string;
+
+  @Column({
+    type: 'enum',
+    enum: GenreType,
+    enumName: 'genre_type',
+    nullable: true,
+    name: 'genre'
+  })
+  gender?: GenreType;
+
+  @Column({ type: 'date', nullable: true, name: 'date_naissance' })
+  birth_date?: Date;
+
+  @Column({ type: 'date', nullable: true, name: 'date_prevue_naissance' })
+  due_date?: Date;
+
+  @Column({ nullable: true, name: 'photo_url', type: 'text' })
+  photo_url?: string;
+
+  @Column({ default: false, name: 'consentement_photo', type: 'boolean' })
+  consent_photo: boolean;
+
+  @Column({ type: 'timestamptz', nullable: true, name: 'date_consentement_photo' })
+  consent_photo_at?: Date;
+
+  @Column({ default: false, name: 'est_multiple', type: 'boolean' })
+  is_multiple: boolean;
+
+  // Lien via table de jointure enfants_parents
+  @OneToMany(() => ParentsChildren, pc => pc.child)
+  parentLinks: ParentsChildren[];
+
+  // Relation avec Dossier
+  @OneToMany(() => Dossier, d => d.child)
+  dossiers: Dossier[];
+}