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/routes/relais/dto/create-relais.dto.ts

@@ -0,0 +1,34 @@
+import { ApiProperty } from '@nestjs/swagger';
+import { IsBoolean, IsNotEmpty, IsOptional, IsString, IsObject } from 'class-validator';
+
+export class CreateRelaisDto {
+  @ApiProperty({ example: 'Relais Petite Enfance Centre' })
+  @IsString()
+  @IsNotEmpty()
+  nom: string;
+
+  @ApiProperty({ example: '12 rue de la Mairie, 75000 Paris' })
+  @IsString()
+  @IsNotEmpty()
+  adresse: string;
+
+  @ApiProperty({ example: { lundi: '09:00-17:00' }, required: false })
+  @IsOptional()
+  @IsObject()
+  horaires_ouverture?: any;
+
+  @ApiProperty({ example: '0123456789', required: false })
+  @IsOptional()
+  @IsString()
+  ligne_fixe?: string;
+
+  @ApiProperty({ default: true, required: false })
+  @IsOptional()
+  @IsBoolean()
+  actif?: boolean;
+
+  @ApiProperty({ example: 'Notes internes...', required: false })
+  @IsOptional()
+  @IsString()
+  notes?: string;
+}