webapp: drop rig:playlist pipeline, source track count from mpc stats

The four overlays that read /data/playlist.js (loading, goodbye,
music-box, music/nc) only ever consumed `tracks.length` for cosmetic
"LIBRARY :: N TRACKS" / "indexed N tracks" flavor text — all live
playback signal flows through bridges/mpd-state.py over OBS WS. The
142 KB JSON, ffprobe walk, and ETag-cached route were all producing
one integer that MPD itself already knows.

RigData::playlistCount() now shells `mpc stats` and parses "Songs: N",
returning 0 on any failure (treated by callers as empty library).
Removes RigPlaylistCommand, DataController::playlist(), the
/data/playlist.js route, the per-overlay <script src> + window.__PLAYLIST
shims, and the stale storage/data/playlist.json artifact.

AudioController still consumes config('rig.music_dirs') for the HTTP
audio stream — that's orthogonal and stays.

webapp/app/Http/Controllers/DataController.php

@@ -3,53 +3,10 @@
 namespace App\Http\Controllers;
 
 use App\Support\RigData;
-use Illuminate\Http\Request;
-use Illuminate\Http\Response;
-use Symfony\Component\HttpFoundation\BinaryFileResponse;
 use Symfony\Component\HttpFoundation\Response as SymfonyResponse;
 
 class DataController extends Controller
 {
-    /**
-     * Serve the playlist as a script-tag-friendly JS global. Cached via ETag on file mtime
-     * so CEF can revalidate cheaply (the playlist file changes rarely but the body is ~142 KB).
-     */
-    public function playlist(Request $request, RigData $rig)
-    {
-        $path = $rig->playlistPath();
-        $tracks = $rig->playlist();
-        $mtime = is_file($path) ? filemtime($path) : 0;
-        $etag = '"' . md5('playlist:' . $mtime) . '"';
-
-        if ($request->headers->get('If-None-Match') === $etag) {
-            return response('', 304)->header('ETag', $etag);
-        }
-
-        // Rewrite `file://` URIs into `/audio?p=...` HTTP URLs so the
-        // music-daemon page (served over HTTP) can load tracks. Chromium
-        // blocks HTTP-origin pages from loading file:// media.
-        if (isset($tracks['tracks']) && is_array($tracks['tracks'])) {
-            foreach ($tracks['tracks'] as $i => $track) {
-                if (!isset($track['file'])) continue;
-                if (str_starts_with($track['file'], 'file://')) {
-                    $absolute = rawurldecode(substr($track['file'], 7));
-                    $tracks['tracks'][$i]['file'] = \App\Http\Controllers\AudioController::urlFor($absolute);
-                }
-            }
-        }
-
-        $body = 'window.__PLAYLIST = ' . json_encode(
-            $tracks,
-            JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE
-        ) . ';';
-
-        return response($body, 200, [
-            'Content-Type'  => 'application/javascript; charset=utf-8',
-            'Cache-Control' => 'public, must-revalidate',
-            'ETag'          => $etag,
-        ]);
-    }
-
     /**
      * Serve bridges/cover.jpg. `no-store` so CEF never holds a stale image
      * even if a caller forgets the ?v=<hash> cache-bust. 404 returns a 1×1