Chunked video upload, persistent track order, per-track playlist entries

Chunked uploads: bypass Cloudflare's 100 MB request cap by slicing the
video/audio into 8 MB chunks and reassembling server-side before the
normal store flow runs.

Track reorder: audio tracks gain a `position` column so a user's edit-
modal ordering survives reload. `Video::audioTracks()` now orders by
position, `promote_track_id` remembers the swapped row, and freshly
uploaded tracks append to the end.

Playlist per-track pinning: `playlist_videos.audio_track_id` remembers
which language the user pinned when adding a song. Same song with a
different track becomes a separate row (Spotify-style duplicates).
Player-data exposes `active_stream_url` + `active_track_id`, sidebar
cards render `?track=` from the pivot, and both `plTransitionTo` and
initial-load code activate the corresponding language option.

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

app/Models/Playlist.php

@@ -34,7 +34,7 @@ class Playlist extends Model
     public function videos()
     {
         return $this->belongsToMany(Video::class, 'playlist_videos')
-            ->withPivot('position', 'watched_seconds', 'watched', 'added_at', 'last_watched_at')
+            ->withPivot('position', 'audio_track_id', 'watched_seconds', 'watched', 'added_at', 'last_watched_at')
             ->orderBy('position');
     }
 
@@ -296,24 +296,48 @@ class Playlist extends Model
         }
     }
 
-    // Add video to playlist
-    public function addVideo(Video $video)
+    // Add video to playlist. When $audioTrackId is null the primary track
+    // plays; otherwise the specified language track is pinned to this row.
+    // Same video with a *different* track becomes a separate row.
+    public function addVideo(Video $video, ?int $audioTrackId = null)
     {
-        if ($this->hasVideo($video)) {
+        if ($this->hasVideoWithTrack($video, $audioTrackId)) {
             return false;
         }
 
         $maxPosition = $this->videos()->max('position') ?? -1;
 
         $this->videos()->attach($video->id, [
-            'position' => $maxPosition + 1,
-            'added_at' => now(),
+            'position'       => $maxPosition + 1,
+            'audio_track_id' => $audioTrackId,
+            'added_at'       => now(),
         ]);
 
         return true;
     }
 
-    // Remove video from playlist
+    // Remove a specific (video, track) row from the playlist. When
+    // $audioTrackId is null, only the "primary track" row is removed —
+    // language-pinned rows for the same video are left in place.
+    public function removeVideoWithTrack(Video $video, ?int $audioTrackId = null)
+    {
+        $query = \DB::table('playlist_videos')
+            ->where('playlist_id', $this->id)
+            ->where('video_id', $video->id);
+        if ($audioTrackId === null) {
+            $query->whereNull('audio_track_id');
+        } else {
+            $query->where('audio_track_id', $audioTrackId);
+        }
+        $deleted = $query->delete();
+
+        if ($deleted) $this->reorderPositions();
+
+        return (bool) $deleted;
+    }
+
+    // Remove *all* rows for a given video (any track). Preserved for
+    // callers that don't care about the track distinction.
     public function removeVideo(Video $video)
     {
         if (! $this->hasVideo($video)) {
@@ -328,6 +352,21 @@ class Playlist extends Model
         return true;
     }
 
+    // Does this playlist contain (video, track)? track=null matches the
+    // "primary track" row specifically, not any row for the video.
+    public function hasVideoWithTrack(Video $video, ?int $audioTrackId = null): bool
+    {
+        $query = \DB::table('playlist_videos')
+            ->where('playlist_id', $this->id)
+            ->where('video_id', $video->id);
+        if ($audioTrackId === null) {
+            $query->whereNull('audio_track_id');
+        } else {
+            $query->where('audio_track_id', $audioTrackId);
+        }
+        return $query->exists();
+    }
+
     // Reorder positions after removal
     protected function reorderPositions()
     {