feat(products): implement category selection and product creation in receipt import

frontend/app/api/products/[id]/route.ts

@@ -0,0 +1,16 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getAuthHeaders } from '../../../../lib/auth-headers';
+
+const API_BASE = process.env.NEXT_PUBLIC_API_URL_INTERNAL || 'http://recipe-api:8080';
+
+export async function PATCH(req: NextRequest, { params }: { params: { id: string } }) {
+  const authHeaders = await getAuthHeaders();
+  const body = await req.json();
+  const res = await fetch(`${API_BASE}/api/products/${params.id}`, {
+    method: 'PATCH',
+    headers: { 'Content-Type': 'application/json', ...authHeaders },
+    body: JSON.stringify(body),
+  });
+  const data = await res.json().catch(() => ({}));
+  return NextResponse.json(data, { status: res.status });
+}