Audio songs: one-folder storage, version-aware download/share, GPU-checked renders

Storage structure
- All audio tracks (primary + per-language) now live in one folder per song with
  unique lowercase names ({slug}-{lang}-{id}); no more tracks/ subfolder.
- Generated renders (download video + HLS) moved into the song's local-only cache/
  subfolder, separated from source files (never synced to NAS, safe to wipe).
- tracks:reorganize artisan command (dry-run default) consolidates legacy files,
  updates DB paths, and deletes orphans + empty folders.
- CLAUDE.md documents the canonical layout as a global rule (identical local + NAS).

Version-aware download & share
- Download MP3/Video and Share now act on the version being played; ?track={id}
  is carried through share links and auto-selects audio + title + flag + about +
  OG/meta on open.

GPU + visualizer
- Setting::gpuUsable() runs a cached health probe (nvidia-smi + nvenc smoke test,
  256x144) before sending any encode to the GPU; falls back to CPU otherwise.
- Visualizer "Download Video" bakes in equal-width, cover-coloured, translucent
  frequency bars; loop-filter rebuild makes generation ~25x faster.

Image cropper
- result-callback mode + per-song cover-slide cropper in upload/edit (modal + mobile).

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

app/Http/Controllers/SuperAdminController.php

@@ -884,6 +884,9 @@ class SuperAdminController extends Controller
         Setting::set('gpu_preset',    $request->gpu_preset);
         Setting::set('ffmpeg_binary', $binary);
 
+        // GPU config changed — drop the cached health-check so the next encode re-probes.
+        Setting::flushGpuProbe();
+
         return back()->with('success', 'Settings saved.');
     }
 
@@ -924,21 +927,9 @@ class SuperAdminController extends Controller
      */
     private function probeNvenc(): bool
     {
-        $ffmpeg = Setting::ffmpegBinary();
-        $tmp    = sys_get_temp_dir() . '/nvenc_probe_' . getmypid() . '.mp4';
-        $device = Setting::gpuDevice();
-
-        exec(
-            escapeshellcmd($ffmpeg)
-            . ' -f lavfi -i nullsrc=s=128x72:r=1 -frames:v 1'
-            . " -c:v h264_nvenc -gpu {$device}"
-            . ' -y ' . escapeshellarg($tmp) . ' 2>/dev/null',
-            $out, $exit
-        );
-
-        $ok = ($exit === 0 && file_exists($tmp) && filesize($tmp) > 0);
-        @unlink($tmp);
-        return $ok;
+        // Single source of truth lives on the Setting model; force the NVENC encoder so the
+        // admin indicator always reflects GPU capability regardless of the configured encoder.
+        return Setting::probeGpu('h264_nvenc');
     }
 
     public function nasStorage()