feat(player): stream audio by default, add [audio] config for cookies and downloads

Long tracks (15 min to 1 hour+) didnt playbecause every song was fully
downloaded with yt-dlp into the cache before mpv was started.

Resolve the direct media URL with yt-dlp -g and hand it to mpv, so
playback starts within a couple of seconds. Cached files are still
used when present.

Add an [audio] section to config.toml:
- download: download songs to the cache before playing (default false,
  i.e. stream). Prefetch of the next track only runs in this mode.
- download_max_minutes: in download mode, songs longer than this (or of
  unknown length) are still streamed so 0 means no limit. default is le 15.
- cookies_from_browser: passed to yt-dlp as --cookies-from-browser for
  playback, for when YouTube asks to sign in or blocks a song.

src/player.rs

@@ -6,6 +6,8 @@ use std::time::{Duration, Instant};
 use anyhow::{anyhow, bail, Result};
 use serde_json::{json, Value};
 
+use crate::config::Audio;
+
 /// Platform-specific transport for mpv's JSON IPC.
 /// Unix: a Unix domain socket. Windows: a named pipe (`\\.\pipe\...`).
 #[cfg(unix)]
@@ -311,6 +313,15 @@ impl Drop for Player {
 
 const KEEP_FILES: usize = 40;
 
+/// Base yt-dlp command with the user's cookie setting applied.
+fn ytdlp(audio: &Audio) -> Command {
+    let mut cmd = Command::new("yt-dlp");
+    if let Some(browser) = audio.cookies() {
+        cmd.arg("--cookies-from-browser").arg(browser);
+    }
+    cmd
+}
+
 fn audio_dir() -> PathBuf {
     dirs::cache_dir()
         .unwrap_or_else(std::env::temp_dir)
@@ -326,13 +337,13 @@ pub fn cached_audio(id: &str) -> Option<PathBuf> {
         .find(|p| p.file_stem().and_then(|s| s.to_str()) == Some(id))
 }
 
-pub fn fetch_audio(id: &str) -> Result<PathBuf, String> {
+pub fn fetch_audio(id: &str, audio: &Audio) -> Result<PathBuf, String> {
     if let Some(path) = cached_audio(id) {
         return Ok(path);
     }
     let dir = audio_dir();
     std::fs::create_dir_all(&dir).map_err(|e| format!("can't create {}: {e}", dir.display()))?;
-    let mut cmd = Command::new("yt-dlp");
+    let mut cmd = ytdlp(audio);
     cmd.args(["-f", "bestaudio/best", "--no-playlist", "--no-warnings", "--no-progress", "--no-mtime"])
         .arg("-P")
         .arg(&dir)
@@ -357,6 +368,35 @@ pub fn fetch_audio(id: &str) -> Result<PathBuf, String> {
         .unwrap_or_else(|| "yt-dlp downloaded nothing".into()))
 }
 
+/// Ask yt-dlp for the direct media URL so mpv can start playing right away
+/// instead of waiting for the whole file to download.
+pub fn resolve_stream(id: &str, audio: &Audio) -> Result<String, String> {
+    let mut cmd = ytdlp(audio);
+    cmd.args(["-f", "bestaudio/best", "--no-playlist", "--no-warnings", "-g"])
+        .arg(format!("https://music.youtube.com/watch?v={id}"))
+        .stdin(Stdio::null());
+    crate::sys::no_window(&mut cmd);
+    let out = cmd
+        .output()
+        .map_err(|e| format!("could not run yt-dlp ({e}); is it installed and on PATH?"))?;
+    let stdout = String::from_utf8_lossy(&out.stdout);
+    if let Some(url) = stdout
+        .lines()
+        .map(str::trim)
+        .find(|l| l.starts_with("http"))
+        .filter(|_| out.status.success())
+    {
+        return Ok(url.to_string());
+    }
+    let stderr = String::from_utf8_lossy(&out.stderr);
+    Err(stderr
+        .lines()
+        .rev()
+        .find_map(|l| l.strip_prefix("ERROR: "))
+        .map(ytdl_reason)
+        .unwrap_or_else(|| "yt-dlp returned no stream URL".into()))
+}
+
 fn prune(dir: &std::path::Path) {
     let Ok(entries) = std::fs::read_dir(dir) else {
         return;