feat(backend): implement Relais module and relation with Gestionnaire (Ticket #94)

- Create Relais entity
- Create Relais module, controller, service with CRUD
- Update Users entity with ManyToOne relation to Relais
- Update GestionnairesService to handle relaisId

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

backend/src/entities/users.entity.ts

@@ -1,11 +1,12 @@
 import {
   Entity, PrimaryGeneratedColumn, Column,
   CreateDateColumn, UpdateDateColumn,
-  OneToOne, OneToMany
+  OneToOne, OneToMany, ManyToOne, JoinColumn
 } from 'typeorm';
 import { AssistanteMaternelle } from './assistantes_maternelles.entity';
 import { Parents } from './parents.entity';
 import { Message } from './messages.entity';
+import { Relais } from './relais.entity';
 
 // Enums alignés avec la BDD PostgreSQL
 export enum RoleType {
@@ -147,4 +148,11 @@ export class Users {
 
   @OneToMany(() => Parents, parent => parent.co_parent)
   co_parent_in?: Parents[];
+
+  @Column({ nullable: true, name: 'relais_id' })
+  relaisId?: string;
+
+  @ManyToOne(() => Relais, relais => relais.gestionnaires, { nullable: true })
+  @JoinColumn({ name: 'relais_id' })
+  relais?: Relais;
 }