feat: P7 在线播放（播放队列、媒体控制）与自建歌单

- 播放器：统一 PlayItem 队列，顺序 / 列表循环 / 单曲循环 / 随机，滚动歌词含翻译，Media Session，队列与进度存 localStorage
- 在线播放音质可在设置中选择；曲库已有的歌优先播放本地文件
- 自建歌单：混排在线曲目与本地文件，拖动排序，一键下载曲库缺失曲目

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

server/src/stream.ts

@@ -1,19 +1,26 @@
-// 试听代理：解析出 320K 音源后由服务端转发（支持 Range），绕过防盗链与混合内容
+// 在线播放代理：按设置的播放音质解析音源后由服务端转发（支持 Range），绕过防盗链与混合内容
 import { Readable } from 'node:stream';
 import type { Context } from 'koa';
 import { UA } from './core/net/http.ts';
 import { getProvider } from './core/providers/index.ts';
+import type { QualityKey } from './core/quality.ts';
 import { TtlCache } from './core/util.ts';
+import { getSettings } from './settings.ts';
 
-const urlCache = new TtlCache<{ url: string; ext: string }>(3 * 60 * 1000, 200);
+// 音源直链通常有几分钟到几小时的有效期；拖动进度条时每个 Range 请求都会命中缓存
+const urlCache = new TtlCache<{ url: string; ext: string; quality: QualityKey }>(3 * 60 * 1000, 200);
 const MIME: Record<string, string> = { mp3: 'audio/mpeg', flac: 'audio/flac', m4a: 'audio/mp4', ogg: 'audio/ogg' };
 
 export async function proxyStream(ctx: Context, source: string, id: string) {
   const provider = getProvider(source);
-  const audio = await urlCache.getOrSet(`${source}:${id}`, async () => {
-    const r = await provider.resolveAudio(id, 'high');
-    return { url: r.url, ext: r.ext };
-  });
+  const quality = getSettings().playQuality;
+  const audio = await urlCache
+    .getOrSet(`${source}:${id}:${quality}`, async () => {
+      const r = await provider.resolveAudio(id, quality);
+      return { url: r.url, ext: r.ext, quality: r.quality };
+    })
+    // 版权下架等情况很常见，播放器会自动跳过，不必按服务端错误记日志
+    .catch((e: Error) => ctx.throw(404, e.message));
 
   const controller = new AbortController();
   ctx.req.on('close', () => controller.abort());
@@ -26,6 +33,7 @@ export async function proxyStream(ctx: Context, source: string, id: string) {
   ctx.set('Content-Type', MIME[audio.ext] || upstream.headers.get('content-type') || 'application/octet-stream');
   ctx.set('Accept-Ranges', 'bytes');
   ctx.set('Cache-Control', 'no-store');
+  ctx.set('X-Audio-Quality', audio.quality);
   for (const h of ['content-length', 'content-range']) {
     const v = upstream.headers.get(h);
     if (v) ctx.set(h, v);