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]>

database/migrations/2026_07_31_000001_add_position_to_video_audio_tracks.php

@@ -0,0 +1,30 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('video_audio_tracks', function (Blueprint $table) {
+            $table->unsignedInteger('position')->default(0)->after('label');
+            $table->index(['video_id', 'position']);
+        });
+
+        // Backfill existing rows so their current id-order becomes the
+        // canonical position. New rows start at 0 and get placed at the
+        // end by the update handler.
+        DB::statement('UPDATE video_audio_tracks SET position = id');
+    }
+
+    public function down(): void
+    {
+        Schema::table('video_audio_tracks', function (Blueprint $table) {
+            $table->dropIndex(['video_id', 'position']);
+            $table->dropColumn('position');
+        });
+    }
+};

database/migrations/2026_07_31_000002_add_audio_track_id_to_playlist_videos.php

@@ -0,0 +1,33 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('playlist_videos', function (Blueprint $table) {
+            // Nullable — null means "play the primary track".
+            $table->unsignedBigInteger('audio_track_id')
+                ->nullable()
+                ->after('video_id');
+
+            // Drop the old (playlist_id, video_id) uniqueness so the same
+            // video can appear multiple times with different tracks.
+            $table->dropUnique(['playlist_id', 'video_id']);
+
+            $table->index(['playlist_id', 'video_id', 'audio_track_id'], 'playlist_video_track_idx');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('playlist_videos', function (Blueprint $table) {
+            $table->dropIndex('playlist_video_track_idx');
+            $table->unique(['playlist_id', 'video_id']);
+            $table->dropColumn('audio_track_id');
+        });
+    }
+};