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/Jobs/CompressVideoJob.php

@@ -51,7 +51,9 @@ class CompressVideoJob implements ShouldQueue
             ]);
             $ffmpegVideo = $ffmpeg->open($originalPath);
 
-            $gpuEnabled = Setting::gpuEnabled();
+            // Verify the GPU is actually reachable and able to encode before sending
+            // the file to it; otherwise fall back to CPU so the job never hangs.
+            $gpuEnabled = Setting::gpuUsable();
             $encoder    = Setting::gpuEncoder();
             $preset     = Setting::gpuPreset();
             $device     = Setting::gpuDevice();