feat(shorts): /shorts/{id} deep-link + URL sync + persistent mute + wheel nav

- New route /shorts/{video} opens the feed scrolled to that short.
  Controller aborts 404 when the id doesn't resolve to a short or
  isn't viewable by the current viewer, so bad links land on the
  branded 404 (added in the next commit) rather than loading an
  empty feed.
- The IntersectionObserver that detects the active short now
  history.replaceState()s the URL to /shorts/{id} so copy-paste of
  the address bar works, without pushing a navigation entry — the
  back button still exits the feed in one step.
- Mute state is persisted in localStorage (shortsMuted = '0' | '1')
  so unmuting once sticks across sessions. Default remains muted
  to satisfy autoplay policies on first load.
- Mouse-wheel navigation moves one short per gesture with a 450 ms
  debounce. Trackpad flicks no longer skip five shorts at once.

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

app/Http/Controllers/VideoController.php

@@ -26,7 +26,7 @@ class VideoController extends Controller
 {
     public function __construct()
     {
-        $this->middleware('auth')->except(['index', 'show', 'search', 'stream', 'hls', 'trending', 'shorts', 'download', 'downloadMp3', 'recordShare', 'ogImage', 'vsPreview', 'accessShare', 'showByToken', 'recommendations', 'slideshowProgress', 'playerData', 'streamAudioTrack', 'lyricsProgress', 'translateDescription', 'feedMore']);
+        $this->middleware('auth')->except(['index', 'show', 'search', 'stream', 'hls', 'trending', 'shorts', 'shortsFocused', 'download', 'downloadMp3', 'recordShare', 'ogImage', 'vsPreview', 'accessShare', 'showByToken', 'recommendations', 'slideshowProgress', 'playerData', 'streamAudioTrack', 'lyricsProgress', 'translateDescription', 'feedMore']);
     }
 
     /**
@@ -2190,7 +2190,7 @@ class VideoController extends Controller
         ]);
     }
 
-    public function shorts(Request $request)
+    public function shorts(Request $request, ?int $startId = null)
     {
         $videos = Video::public()
             ->where('is_shorts', true)
@@ -2199,7 +2199,23 @@ class VideoController extends Controller
             ->latest()
             ->get();
 
-        return view('videos.shorts', compact('videos'));
+        return view('videos.shorts', [
+            'videos'  => $videos,
+            'startId' => $startId, // the id to auto-scroll to, if any
+        ]);
+    }
+
+    /**
+     * /shorts/{video}: deep-link to a specific short in the vertical feed.
+     * The feed itself is the same ordered list; the view uses ?start= / the
+     * $startId prop to scroll into position on load.
+     */
+    public function shortsFocused(Video $video)
+    {
+        if (! $video->is_shorts || ! $video->canView(Auth::user())) {
+            abort(404);
+        }
+        return $this->shorts(request(), $video->id);
     }
 
     public function stream(Video $video)