fix(player): WinHTTP fallback for /jdymusic/ CDN that drops Node TCP

The old jdymusic CDN (e.g. m701/m801.music.126.net/.../jdymusic/obj/...)
intermittently drops connections from Node's HTTP stack — even with a
browser UA — while the same URL fetched via WinHTTP works. Newer paths
(/jd-musicrep-ts/, /ymusic/) do not have this restriction.

On Windows, dispatch /jdymusic/ URLs through `System.Net.WebClient` in
PowerShell into a temp file, then run ffmpeg against the file. Other
URLs and non-Windows platforms keep the direct ffmpeg + browser-UA path
from the previous commit. Also fix buildFfmpegArgs to omit HTTP-only
flags (-reconnect_*, -headers) when the input is a local file path —
new ffmpeg builds reject these as "Option not found".

stop() now also kills any in-flight PowerShell downloader and removes
the temp dir, so cancellation is clean.

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

scripts/test_jdymusic_powershell.mjs

@@ -0,0 +1,106 @@
+// Empirically verifies the PowerShell-download workaround for jdymusic CDN
+// blocks Node.js HTTP. Runs A/B against the same fresh /jdymusic/ URL:
+//   A) ffmpeg direct with browser UA (the previous fix in this branch)
+//   B) PowerShell WebClient -> temp file -> ffmpeg from file (the new fix)
+// Reports bytes received + exit code + stderr-tail for each.
+
+import { spawn } from "node:child_process";
+import { mkdtempSync, statSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { buildFfmpegArgs } from "../dist/audio/player.js";
+
+const url = process.argv[2];
+if (!url) {
+  console.error("usage: node scripts/test_jdymusic_powershell.mjs <jdymusic_url>");
+  process.exit(2);
+}
+if (!url.includes("/jdymusic/")) {
+  console.error("warning: this script targets /jdymusic/ URLs specifically");
+}
+
+const FFMPEG = "ffmpeg";
+const BROWSER_UA =
+  "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36";
+const TIMEOUT_MS = 20_000;
+
+function runFfmpeg(label, args, stdinSource) {
+  return new Promise((resolve) => {
+    const proc = spawn(FFMPEG, args, { stdio: [stdinSource ?? "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 });
+    });
+  });
+}
+
+function downloadViaPowerShell(targetUrl, outFile) {
+  return new Promise((resolve) => {
+    const psScript = [
+      "$ErrorActionPreference = 'Stop'",
+      "$ProgressPreference = 'SilentlyContinue'",
+      "$wc = New-Object System.Net.WebClient",
+      "$wc.Headers.Add('User-Agent', $env:DL_UA)",
+      "$wc.Headers.Add('Referer', $env:DL_REFERER)",
+      "$wc.DownloadFile($env:DL_URL, $env:DL_OUT)",
+    ].join("; ");
+    const ps = spawn(
+      "powershell",
+      ["-NoProfile", "-ExecutionPolicy", "Bypass", "-Command", psScript],
+      {
+        env: {
+          ...process.env,
+          DL_URL: targetUrl,
+          DL_OUT: outFile,
+          DL_UA: BROWSER_UA,
+          DL_REFERER: "https://music.163.com/",
+        },
+        stdio: ["ignore", "pipe", "pipe"],
+      },
+    );
+    let stderr = "";
+    ps.stderr.on("data", (chunk) => { stderr += chunk.toString(); });
+    ps.on("exit", (code) => resolve({ code, stderr }));
+  });
+}
+
+console.log(`URL: ${url}\n`);
+
+console.log("[A] ffmpeg direct (browser UA via -headers)");
+const a = await runFfmpeg("A", buildFfmpegArgs(url, 0));
+console.log(`    code=${a.code} bytes=${a.bytes} killed=${a.killed}`);
+console.log(`    stderr-tail: ${a.stderrTail.split("\n").slice(-3).join(" | ")}\n`);
+
+console.log("[B] PowerShell WebClient -> temp file -> ffmpeg -i tempfile");
+const tempDir = mkdtempSync(join(tmpdir(), "tsbot-jdymusic-test-"));
+const tempFile = join(tempDir, "song.audio");
+const psStart = Date.now();
+const dl = await downloadViaPowerShell(url, tempFile);
+const psMs = Date.now() - psStart;
+if (dl.code !== 0) {
+  console.log(`    PowerShell download FAILED: code=${dl.code}`);
+  console.log(`    stderr: ${dl.stderr.slice(-500)}`);
+  rmSync(tempDir, { recursive: true, force: true });
+  process.exit(1);
+}
+const dlSize = statSync(tempFile).size;
+console.log(`    PowerShell downloaded ${dlSize} bytes in ${psMs}ms`);
+
+const b = await runFfmpeg("B", buildFfmpegArgs(tempFile, 0));
+console.log(`    ffmpeg-from-file: code=${b.code} bytes=${b.bytes} killed=${b.killed}`);
+console.log(`    stderr-tail: ${b.stderrTail.split("\n").slice(-3).join(" | ")}\n`);
+
+rmSync(tempDir, { recursive: true, force: true });
+
+const aBlocked = a.bytes === 0 && !a.killed;
+const bWorked = b.bytes > 100_000;
+console.log(
+  `Verdict: direct ${aBlocked ? "BLOCKED" : "OK"} ; ` +
+  `powershell-then-ffmpeg ${bWorked ? "WORKED" : "FAILED"}`,
+);