perf(feeds): cursor-paginated infinite scroll on /videos

Add VideoController@feedMore -> JSON { items, next_cursor, has_more }
that pages the current filter (all / shorts / match / music / lang:xx)
with Laravel's cursorPaginate(24). Cursor is stable across inserts, so
scrolling never duplicates or skips a video when something is uploaded
mid-session.

Client side: a #feed-sentinel + IntersectionObserver (rootMargin
400px) appends the next page of cards to the existing grid without a
page reload. A Load More button is always wired as the fallback when
IO is unavailable or a fetch fails. Both reuse the existing
<x-video-card/> component, so the newly fetched cards get the same
singleton edit modal + width/height thumbs as the server-rendered ones.

The initial 60-card server render stays, so the first viewport is
unchanged. The limit(60) and limit(50) caps in index() can now be
treated as "first page size" rather than a hard ceiling.

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

routes/web.php

@@ -24,6 +24,7 @@ Route::get('/', [VideoController::class, 'index'])->name('home');
 
 // Video routes - public
 Route::get('/videos', [VideoController::class, 'index'])->name('videos.index');
+Route::get('/videos/feed/more', [VideoController::class, 'feedMore'])->name('videos.feed.more');
 Route::get('/videos/search', [VideoController::class, 'search'])->name('videos.search');
 Route::get('/trending', [VideoController::class, 'trending'])->name('videos.trending');
 Route::get('/shorts', [VideoController::class, 'shorts'])->name('videos.shorts');