feat: add multipart image uploads

Register Fastify multipart support, validate JPEG/PNG/WebP binary signatures, store upload bytes through ImageStorage, persist metadata after storage succeeds, clean up bytes on metadata failure, and document the upload boundary. Verification: npm test passed 68 tests and integration passed 14 tests. No build script is configured.

apps/api/src/app/build-app.js

@@ -1,5 +1,6 @@
 import Fastify from 'fastify';
 import cookie from '@fastify/cookie';
+import multipart from '@fastify/multipart';
 
 import { registerAuthRoutes } from '../modules/auth/routes/auth-routes.js';
 import { registerAdminInventoryRoutes } from '../modules/inventory/routes/admin-inventory-routes.js';
@@ -28,6 +29,7 @@ export function buildApp(dependencies) {
 
   app.get('/health', async () => ({ data: { status: 'ok' } }));
   app.register(cookie);
+  app.register(multipart, { limits: { fileSize: 10 * 1024 * 1024, files: 1 } });
   app.register(registerAuthRoutes, {
     ...dependencies,
     prefix: '/api/v1/auth',

apps/api/src/app/server.js

@@ -18,6 +18,7 @@ import { createInventoryItemRepository } from '../modules/inventory/repositories
 import { createInventoryItemService } from '../modules/inventory/services/inventory-item-service.js';
 import { createInventoryImageRepository } from '../modules/inventory/repositories/inventory-image-repository.js';
 import { createInventoryImageService } from '../modules/inventory/services/inventory-image-service.js';
+import { createLocalImageStorage } from '../infrastructure/images/local-image-storage.js';
 import { createConditionRepository } from '../modules/inventory/repositories/condition-repository.js';
 import { createListingRepository } from '../modules/listings/repositories/listing-repository.js';
 import { createListingService } from '../modules/listings/services/listing-service.js';
@@ -78,7 +79,10 @@ async function startServer() {
       inventoryItemRepository,
       productRepository,
     }),
-    inventoryImageService: createInventoryImageService({ inventoryImageRepository }),
+    inventoryImageService: createInventoryImageService({
+      imageStorage: createLocalImageStorage(process.env.IMAGE_STORAGE_ROOT ?? '.local/image-storage'),
+      inventoryImageRepository,
+    }),
     listingService: createListingService({ listingRepository, inventoryImageRepository }),
     productService: createProductService({ productRepository }),
   });