Add multi-language audio tracks and self-hosted flag-icons

Introduce per-video language support and multiple audio tracks
(VideoAudioTrack model + migrations for language, description, title),
a reusable language-select component, and a track-editor form. Bundle
the self-hosted flag-icons v7.2.3 library and a NAS auto-sync command.

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

app/Jobs/NasToLocalMigrationJob.php

@@ -164,6 +164,7 @@ class NasToLocalMigrationJob implements ShouldQueue
 
             // ── Disable NAS ───────────────────────────────────────────────────
             Setting::set('nas_sync_enabled', 'false');
+            app(\App\Services\NasSyncService::class)->flushReachabilityCache();
 
             $progress['done']  = true;
             $progress['phase'] = 'Complete';