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/Support/RigData.php

@@ -2,9 +2,13 @@
 
 namespace App\Support;
 
+use Symfony\Component\Process\Process;
+use Throwable;
+
 class RigData
 {
     private array $cache = [];
+    private ?int $mpdSongCount = null;
 
     public function loading(): array
     {
@@ -23,17 +27,26 @@ class RigData
         ]);
     }
 
-    public function playlist(): array
-    {
-        return $this->read('playlist.json', [
-            'syncedAt' => null, 'sourceDirs' => [], 'trackCount' => 0, 'tracks' => [],
-        ]);
-    }
-
+    /**
+     * Track count from MPD (the live library, queried via `mpc stats`).
+     * Returns 0 if mpc is missing or MPD is unreachable — callers treat
+     * that as "empty library" and degrade their flavor text accordingly.
+     */
     public function playlistCount(): int
     {
-        $p = $this->playlist();
-        return (int) ($p['trackCount'] ?? count($p['tracks'] ?? []));
+        if ($this->mpdSongCount !== null) return $this->mpdSongCount;
+
+        try {
+            $proc = new Process(['mpc', 'stats']);
+            $proc->setTimeout(2);
+            $proc->run();
+            if ($proc->isSuccessful() && preg_match('/^Songs:\s*(\d+)/m', $proc->getOutput(), $m)) {
+                return $this->mpdSongCount = (int) $m[1];
+            }
+        } catch (Throwable) {
+            // fall through
+        }
+        return $this->mpdSongCount = 0;
     }
 
     public function cmd(): array
@@ -49,11 +62,6 @@ class RigData
         return $cmd;
     }
 
-    public function playlistPath(): string
-    {
-        return rtrim(config('rig.storage_data'), '/') . '/playlist.json';
-    }
-
     public function coverPath(): string
     {
         return (string) config('rig.cover_jpg');