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]>

routes/web.php

@@ -70,12 +70,18 @@ Route::post('/videos/{video}/identify', [VideoController::class, 'identify'])->n
 Route::middleware(['auth', 'verified'])->group(function () {
     Route::get('/videos/create', [VideoController::class, 'create'])->name('videos.create');
     Route::post('/videos', [VideoController::class, 'store'])->name('videos.store');
+    Route::post('/videos/upload-chunk', [VideoController::class, 'uploadChunk'])->name('videos.uploadChunk');
     Route::get('/videos/{video}/edit', [VideoController::class, 'edit'])->name('videos.edit');
     Route::put('/videos/{video}', [VideoController::class, 'update'])->name('videos.update');
     Route::post('/videos/{video}/replace-file', [VideoController::class, 'replaceFile'])->name('videos.replaceFile');
     Route::delete('/videos/{video}', [VideoController::class, 'destroy'])->name('videos.destroy');
     Route::delete('/videos/{video}/audio-track/{track}', [VideoController::class, 'deleteAudioTrack'])->name('videos.audio-track.delete');
 
+    // Music-video merge — fold {source} into {target}. Owner-only.
+    Route::get('/videos/{target}/merge/candidates',      [\App\Http\Controllers\VideoMergeController::class, 'candidates'])->name('videos.merge.candidates');
+    Route::get('/videos/{target}/merge/{source}/preview',[\App\Http\Controllers\VideoMergeController::class, 'preview'])->name('videos.merge.preview');
+    Route::post('/videos/{target}/merge/{source}',       [\App\Http\Controllers\VideoMergeController::class, 'merge'])->name('videos.merge');
+
     // Like/unlike routes
     Route::post('/videos/{video}/like', [UserController::class, 'like'])->name('videos.like');
     Route::post('/videos/{video}/unlike', [UserController::class, 'unlike'])->name('videos.unlike');