feat: add storage path helpers

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/storage.js

@@ -0,0 +1,23 @@
+import fs from 'node:fs/promises';
+import path from 'node:path';
+
+export async function ensureStorageDirs(config) {
+  await fs.mkdir(path.join(config.storageDir, 'uploads'), { recursive: true });
+  await fs.mkdir(path.join(config.storageDir, 'outputs'), { recursive: true });
+}
+
+export function uploadPath(config, id, ext) {
+  return path.join(config.storageDir, 'uploads', `${id}.${ext}`);
+}
+
+export function outputPath(config, id, ext) {
+  return path.join(config.storageDir, 'outputs', `${id}.${ext}`);
+}
+
+export async function deleteIfExists(filePath) {
+  try {
+    await fs.unlink(filePath);
+  } catch (error) {
+    if (error.code !== 'ENOENT') throw error;
+  }
+}