feat: expose vip flag on Song for trial-only detection

Add optional vip?: boolean to the Song interface so downstream clients
(e.g. PowerfulTS) can mark copyright-restricted songs that non-VIP users
can only play as a trial fragment, before playback starts.

- provider.ts: add optional vip?: boolean (backward compatible)
- netease.ts: extract mapNeteaseSongs() pure fn; map fee to vip
  (1=VIP, 4=album-only). fee=8 (free low-quality) is excluded because
  it plays in full, just at lower quality.
- qq.ts: mapQqSongs() maps pay.payplay/paytrackprice to vip (one fix
  covers all callers); getDailyRecommendSongs inline mapping too.
- tests: vip mapping assertions for netease fee (1/4=vip, 0/8=free) and
  qq pay fields.

src/music/netease.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest";
-import { parseLyrics, mapNeteaseAlbums } from "./netease.js";
+import { parseLyrics, mapNeteaseAlbums, mapNeteaseSongs } from "./netease.js";
 
 describe("NetEase adapter", () => {
   it("parses LRC format lyrics", () => {
@@ -56,4 +56,25 @@ describe("NetEase adapter", () => {
     expect(mapNeteaseAlbums(null as any)).toEqual([]);
     expect(mapNeteaseAlbums(undefined as any)).toEqual([]);
   });
+
+  it("mapNeteaseSongs maps fee to vip flag (1/4 = vip, 0/8 = free)", () => {
+    const raw = [
+      { id: 1, name: "VIP", ar: [{ name: "A" }], al: { name: "Al", picUrl: "p" }, dt: 180000, fee: 1 },
+      { id: 2, name: "Album-only", ar: [], al: { name: "Al", picUrl: "" }, dt: 0, fee: 4 },
+      { id: 3, name: "Free", ar: [], al: {}, dt: 0, fee: 0 },
+      { id: 4, name: "Free low-quality", ar: [], al: {}, dt: 0, fee: 8 },
+    ];
+    const out = mapNeteaseSongs(raw);
+    expect(out[0].vip).toBe(true);
+    expect(out[1].vip).toBe(true);
+    expect(out[2].vip).toBe(false);
+    expect(out[3].vip).toBe(false); // fee=8 plays in full (low quality), NOT vip
+  });
+
+  it("mapNeteaseSongs accepts artists/album/duration aliases (personal_fm shape)", () => {
+    const out = mapNeteaseSongs([
+      { id: 9, name: "FM", artists: [{ name: "B" }], album: { name: "Al2", picUrl: "p2" }, duration: 200000, fee: 0 },
+    ]);
+    expect(out[0]).toMatchObject({ artist: "B", album: "Al2", coverUrl: "p2", vip: false });
+  });
 });