서버 코드를 Router, Service, Repository 계층으로 분리하고 오류 처리 및 파일 삭제 로직 개선

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/helpers/storage.ts

@@ -0,0 +1,12 @@
+import { mkdir, writeFile } from "fs/promises";
+import { dirname, join } from "path";
+import env from "#lib/server/config.js";
+
+let sequence = 0;
+
+export const createStoredFile = async (content: string | Buffer = "content") => {
+  const path = join(env.libraryPath, "test", `file${++sequence}`);
+  await mkdir(dirname(path), { recursive: true });
+  await writeFile(path, content);
+  return path;
+};