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]>

routes/web.php

@@ -34,6 +34,10 @@ Route::get('/videos/search', function (\Illuminate\Http\Request $request) {
 })->name('videos.search');
 Route::get('/trending', [VideoController::class, 'trending'])->name('videos.trending');
 Route::get('/shorts', [VideoController::class, 'shorts'])->name('videos.shorts');
+// Deep-link form: /shorts/{encoded-id} loads the feed scrolled to that short.
+// The resolveRouteBinding on Video decodes the id; if it's gone, 404 lands
+// on the branded errors/404 page.
+Route::get('/shorts/{video}', [VideoController::class, 'shortsFocused'])->name('videos.shorts.focused');
 Route::get('/videos/create', [VideoController::class, 'create'])->name('videos.create');
 // Redirect legacy numeric video IDs to encoded URLs (backward compatibility)
 Route::get('/videos/{numericId}', function ($numericId) {