feat(#132): POST /enfants staff — parent_user_id + liens foyer.

Autorise GESTIONNAIRE/ADMIN/SUPER_ADMIN à créer un enfant rattaché
à un foyer existant (JSON + parent_user_id). Parent multipart inchangé.

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

backend/src/routes/enfants/enfants.controller.ts

@@ -1,20 +1,33 @@
 import {
   Body,
+  CallHandler,
   Controller,
   Delete,
+  ExecutionContext,
   Get,
+  HttpCode,
+  HttpStatus,
+  Injectable,
+  NestInterceptor,
   Param,
   ParseUUIDPipe,
   Patch,
   Post,
+  UploadedFile,
   UseGuards,
   UseInterceptors,
-  UploadedFile,
 } from '@nestjs/common';
 import { FileInterceptor } from '@nestjs/platform-express';
-import { ApiBearerAuth, ApiTags, ApiConsumes } from '@nestjs/swagger';
+import {
+  ApiBearerAuth,
+  ApiBody,
+  ApiConsumes,
+  ApiOperation,
+  ApiTags,
+} from '@nestjs/swagger';
 import { diskStorage } from 'multer';
 import { extname } from 'path';
+import { Observable } from 'rxjs';
 import { EnfantsService } from './enfants.service';
 import { CreateEnfantsDto } from './dto/create_enfants.dto';
 import { UpdateEnfantsDto } from './dto/update_enfants.dto';
@@ -24,6 +37,47 @@ import { AuthGuard } from 'src/common/guards/auth.guard';
 import { Roles } from 'src/common/decorators/roles.decorator';
 import { RolesGuard } from 'src/common/guards/roles.guard';
 
+const photoMulterOptions = {
+  storage: diskStorage({
+    destination: './uploads/photos',
+    filename: (req, file, cb) => {
+      const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1e9);
+      const ext = extname(file.originalname);
+      cb(null, `enfant-${uniqueSuffix}${ext}`);
+    },
+  }),
+  fileFilter: (req, file, cb) => {
+    if (!file.mimetype.match(/\/(jpg|jpeg|png|gif)$/)) {
+      return cb(new Error('Seules les images sont autorisées'), false);
+    }
+    cb(null, true);
+  },
+  limits: {
+    fileSize: 5 * 1024 * 1024,
+  },
+};
+
+/**
+ * Multer uniquement si Content-Type multipart (parcours parent).
+ * Les appels staff JSON (#132) passent sans interceptor fichier.
+ */
+@Injectable()
+class OptionalEnfantPhotoInterceptor implements NestInterceptor {
+  private readonly multipart = new (FileInterceptor(
+    'photo',
+    photoMulterOptions,
+  ))();
+
+  intercept(context: ExecutionContext, next: CallHandler): Observable<unknown> | Promise<Observable<unknown>> {
+    const req = context.switchToHttp().getRequest();
+    const ct = String(req.headers['content-type'] ?? '');
+    if (!ct.includes('multipart/form-data')) {
+      return next.handle();
+    }
+    return this.multipart.intercept(context, next);
+  }
+}
+
 @ApiBearerAuth('access-token')
 @ApiTags('Enfants')
 @UseGuards(AuthGuard, RolesGuard)
@@ -31,30 +85,22 @@ import { RolesGuard } from 'src/common/guards/roles.guard';
 export class EnfantsController {
   constructor(private readonly enfantsService: EnfantsService) { }
 
-  @Roles(RoleType.PARENT)
-  @Post()
-  @ApiConsumes('multipart/form-data')
-  @UseInterceptors(
-    FileInterceptor('photo', {
-      storage: diskStorage({
-        destination: './uploads/photos',
-        filename: (req, file, cb) => {
-          const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1e9);
-          const ext = extname(file.originalname);
-          cb(null, `enfant-${uniqueSuffix}${ext}`);
-        },
-      }),
-      fileFilter: (req, file, cb) => {
-        if (!file.mimetype.match(/\/(jpg|jpeg|png|gif)$/)) {
-          return cb(new Error('Seules les images sont autorisées'), false);
-        }
-        cb(null, true);
-      },
-      limits: {
-        fileSize: 5 * 1024 * 1024,
-      },
-    }),
+  @Roles(
+    RoleType.PARENT,
+    RoleType.GESTIONNAIRE,
+    RoleType.ADMINISTRATEUR,
+    RoleType.SUPER_ADMIN,
   )
+  @Post()
+  @HttpCode(HttpStatus.CREATED)
+  @ApiOperation({
+    summary: 'Créer un enfant',
+    description:
+      'PARENT : multipart éventuel, rattache au compte connecté. Staff : JSON + parent_user_id (foyer). Ticket #132.',
+  })
+  @ApiConsumes('application/json', 'multipart/form-data')
+  @ApiBody({ type: CreateEnfantsDto })
+  @UseInterceptors(OptionalEnfantPhotoInterceptor)
   create(
     @Body() dto: CreateEnfantsDto,
     @UploadedFile() photo: Express.Multer.File,