feat(spotify): implement milestone M4 importers

skills/spotify/tests/folder.test.ts

@@ -0,0 +1,21 @@
+import assert from "node:assert/strict";
+import { mkdir, mkdtemp, writeFile } from "node:fs/promises";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { test } from "node:test";
+
+import { readFolder } from "../src/importers/folder.js";
+
+test("recursively reads audio filenames and ignores non-audio files", async () => {
+  const root = await mkdtemp(join(tmpdir(), "spotify-folder-"));
+  await mkdir(join(root, "nested"));
+  await writeFile(join(root, "01 - Radiohead - Karma Police.mp3"), "");
+  await writeFile(join(root, "cover.jpg"), "");
+  await writeFile(join(root, "nested", "02 - Massive Attack - Teardrop.flac"), "");
+
+  const refs = await readFolder(root);
+
+  assert.equal(refs.some((ref) => ref.artist === "Radiohead" && ref.title === "Karma Police"), true);
+  assert.equal(refs.some((ref) => ref.artist === "Massive Attack" && ref.title === "Teardrop"), true);
+  assert.equal(refs.some((ref) => ref.source.includes("cover")), false);
+});