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>

scripts/test_netease_ua_fix.mjs

@@ -0,0 +1,73 @@
+// Empirically tests whether the browser UA + Referer headers fix the
+// connection resets we saw in bot.log against m701/m801.music.126.net.
+//
+// Spawns ffmpeg twice against the SAME fresh Netease CDN URL:
+//   A) old args from before the fix (no headers, -reconnect_delay_max 5)
+//   B) new args from after the fix (browser UA + Referer for music.126.net)
+// and reports bytes received + exit code + stderr-tail for each.
+
+import { spawn } from "node:child_process";
+import { buildFfmpegArgs } from "../dist/audio/player.js";
+
+const url = process.argv[2];
+if (!url) {
+  console.error("usage: node scripts/test_netease_ua_fix.mjs <netease_cdn_url>");
+  process.exit(2);
+}
+
+const FFMPEG = "ffmpeg";
+const TIMEOUT_MS = 15_000;
+
+function legacyArgs(u) {
+  return [
+    "-reconnect", "1",
+    "-reconnect_streamed", "1",
+    "-reconnect_delay_max", "5",
+    "-i", u,
+    "-f", "s16le",
+    "-ar", "48000",
+    "-ac", "2",
+    "-acodec", "pcm_s16le",
+    "-",
+  ];
+}
+
+function runFfmpeg(label, args) {
+  return new Promise((resolve) => {
+    const proc = spawn(FFMPEG, args, { stdio: ["ignore", "pipe", "pipe"] });
+    let bytes = 0;
+    let stderrTail = "";
+    let killed = false;
+
+    proc.stdout.on("data", (chunk) => {
+      bytes += chunk.length;
+    });
+    proc.stderr.on("data", (chunk) => {
+      stderrTail = (stderrTail + chunk.toString()).slice(-1500);
+    });
+
+    const timer = setTimeout(() => {
+      killed = true;
+      proc.kill("SIGTERM");
+    }, TIMEOUT_MS);
+
+    proc.on("exit", (code, signal) => {
+      clearTimeout(timer);
+      resolve({ label, bytes, code, signal, killed, stderrTail });
+    });
+  });
+}
+
+console.log(`URL: ${url}\n`);
+
+const a = await runFfmpeg("A) legacy args (no UA)", legacyArgs(url));
+console.log(`[A] code=${a.code} signal=${a.signal} killed=${a.killed} bytes=${a.bytes}`);
+console.log(`    stderr-tail:\n${a.stderrTail.split("\n").slice(-6).map((l) => "    " + l).join("\n")}\n`);
+
+const b = await runFfmpeg("B) fixed args (browser UA + Referer)", buildFfmpegArgs(url, 0));
+console.log(`[B] code=${b.code} signal=${b.signal} killed=${b.killed} bytes=${b.bytes}`);
+console.log(`    stderr-tail:\n${b.stderrTail.split("\n").slice(-6).map((l) => "    " + l).join("\n")}\n`);
+
+const aFailed = a.bytes === 0 && !a.killed && a.code !== 0;
+const bWorked = b.bytes > 100_000; // got real audio bytes
+console.log(`Verdict: legacy ${aFailed ? "FAILED (no bytes, exit code 1)" : "??"} ; fixed ${bWorked ? "WORKED (received audio)" : "??"}`);