fix(player): set browser UA + Referer for Netease CDN to stop auto-skip

Netease's m701/m801.music.126.net CDN RST connections from FFmpeg's
default Lavf UA. The bot's frame loop treats an early ffmpeg exit as
trackEnd and advances the queue, which surfaced as songs auto-skipping
mid-playlist. Add a browser UA + music.163.com Referer for these URLs,
extract args into a tested buildFfmpegArgs(), and harden reconnect
flags (delay_max 5 -> 30, plus reconnect_on_network_error /
reconnect_on_http_error). Verified by A/B running ffmpeg against the
same fresh CDN URL: legacy args got 0 bytes + "End of file" reading
HTTP response; fixed args streamed the full track to completion.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/audio/player.test.ts

@@ -0,0 +1,68 @@
+import { describe, it, expect } from "vitest";
+import { buildFfmpegArgs } from "./player.js";
+
+function getHeadersArg(args: string[]): string {
+  const idx = args.indexOf("-headers");
+  if (idx === -1) return "";
+  return args[idx + 1] ?? "";
+}
+
+describe("buildFfmpegArgs", () => {
+  it("includes browser User-Agent and Referer for Netease CDN URLs", () => {
+    const url = "http://m701.music.126.net/some/path/song.mp3?vuutv=abc";
+    const args = buildFfmpegArgs(url, 0);
+    const headers = getHeadersArg(args);
+    expect(headers).toContain("User-Agent:");
+    expect(headers).toContain("Mozilla/5.0");
+    expect(headers).toContain("Referer: https://music.163.com/");
+  });
+
+  it("keeps Bilibili Referer + UA for bilibili URLs", () => {
+    const url = "https://upos-sz-mirrorcoso1.bilivideo.com/foo/bar.mp3";
+    const args = buildFfmpegArgs(url, 0);
+    const headers = getHeadersArg(args);
+    expect(headers).toContain("Referer: https://www.bilibili.com");
+    expect(headers).toContain("User-Agent: Mozilla/5.0");
+  });
+
+  it("does not set custom headers for unknown URLs", () => {
+    const url = "https://example.com/song.mp3";
+    const args = buildFfmpegArgs(url, 0);
+    expect(args).not.toContain("-headers");
+  });
+
+  it("includes resilient reconnect flags for all URLs", () => {
+    const args = buildFfmpegArgs("https://example.com/song.mp3", 0);
+    expect(args).toContain("-reconnect");
+    expect(args).toContain("-reconnect_streamed");
+    expect(args).toContain("-reconnect_delay_max");
+    expect(args).toContain("-reconnect_on_network_error");
+    expect(args).toContain("-reconnect_on_http_error");
+    const idx = args.indexOf("-reconnect_delay_max");
+    expect(Number(args[idx + 1])).toBeGreaterThanOrEqual(30);
+  });
+
+  it("inserts -ss before -i when seekSeconds > 0", () => {
+    const args = buildFfmpegArgs("https://example.com/song.mp3", 42);
+    const ssIdx = args.indexOf("-ss");
+    const iIdx = args.indexOf("-i");
+    expect(ssIdx).toBeGreaterThan(-1);
+    expect(args[ssIdx + 1]).toBe("42");
+    expect(ssIdx).toBeLessThan(iIdx);
+  });
+
+  it("does not insert -ss when seekSeconds is 0", () => {
+    const args = buildFfmpegArgs("https://example.com/song.mp3", 0);
+    expect(args).not.toContain("-ss");
+  });
+
+  it("ends args with the input URL and PCM output spec", () => {
+    const url = "https://example.com/song.mp3";
+    const args = buildFfmpegArgs(url, 0);
+    const iIdx = args.indexOf("-i");
+    expect(args[iIdx + 1]).toBe(url);
+    expect(args).toContain("-f");
+    expect(args).toContain("s16le");
+    expect(args[args.length - 1]).toBe("-");
+  });
+});