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/tests/application/inventory-image-service.test.js

@@ -0,0 +1,58 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { createInventoryImageService } from '../../src/modules/inventory/services/inventory-image-service.js';
+
+const input = {
+  inventoryItemId: 'inventory-item-id',
+  sellerId: 'seller-id',
+  storageKey: 'inventory/item/front.jpg',
+  originalFilename: 'front.jpg',
+  mimeType: 'image/jpeg',
+  fileSize: 4,
+  width: 1200,
+  height: 900,
+  data: Buffer.from([0xff, 0xd8, 0xff, 0x00]),
+};
+
+test('stores validated upload bytes before persisting image metadata', async () => {
+  const stored = [];
+  const service = createInventoryImageService({
+    imageStorage: {
+      async put(value) { stored.push(value); },
+      async delete() {},
+    },
+    inventoryImageRepository: {
+      async createForSeller(image) {
+        return { id: 'image-1', ...image };
+      },
+    },
+  });
+
+  const image = await service.upload(input);
+
+  assert.equal(stored.length, 1);
+  assert.deepEqual(stored[0], { key: input.storageKey, data: input.data });
+  assert.equal(image.id, 'image-1');
+  assert.equal(image.processingStatus, 'PENDING');
+  assert.equal('data' in image, false);
+});
+
+test('removes stored bytes when metadata persistence fails', async () => {
+  const deleted = [];
+  const service = createInventoryImageService({
+    imageStorage: {
+      async put() {},
+      async delete(key) { deleted.push(key); },
+    },
+    inventoryImageRepository: {
+      async createForSeller() { return null; },
+    },
+  });
+
+  await assert.rejects(
+    () => service.upload(input),
+    (error) => error.code === 'INVENTORY_ITEM_NOT_FOUND',
+  );
+  assert.deepEqual(deleted, [input.storageKey]);
+});