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]>

resources/views/videos/index.blade.php

@@ -211,6 +211,17 @@
     @endif
 
 @endif
+
+{{-- Infinite-scroll sentinel. The IntersectionObserver down in @section('scripts')
+     fetches the next cursor page when this comes into view and appends the
+     rendered cards to the grid above. A visible "Load more" button is the
+     always-available fallback. --}}
+<div id="feed-sentinel"
+     data-feed-filter="{{ $filter ?? 'all' }}"
+     style="height:1px;"></div>
+<div id="feed-loadmore-wrap" style="display:none; text-align:center; padding:16px 0;">
+    <button type="button" id="feed-loadmore" class="action-btn">Load more</button>
+</div>
 </div>{{-- /filter-content --}}
 
 @endsection
@@ -354,5 +365,69 @@
         if (e.state && e.state.filterUrl) swapTo(e.state.filterUrl, false);
     });
 })();
+
+/* ─── Cursor-paginated infinite scroll ───────────────────────────────────
+   The server renders the first page of 60 cards. Everything after that is
+   fetched here, one 24-card page at a time, when the #feed-sentinel scrolls
+   into view. The sentinel sits right after the grid, so we never fetch
+   until the user has actually scrolled past the first page.
+
+   State lives on #feed-sentinel.dataset so a SPA filter-swap can reset it
+   without having to rebind listeners. Fallback: an always-visible "Load
+   more" button that users without IntersectionObserver can click. */
+(function () {
+    const sentinel = document.getElementById('feed-sentinel');
+    const grid     = document.querySelector('.yt-video-grid');
+    const btnWrap  = document.getElementById('feed-loadmore-wrap');
+    const btn      = document.getElementById('feed-loadmore');
+    if (!sentinel || !grid) return;
+
+    let cursor = '';     // null token = next request is the first continuation page
+    let busy   = false;
+    let done   = false;
+    const filter = sentinel.dataset.feedFilter || 'all';
+
+    async function loadMore() {
+        if (busy || done) return;
+        busy = true;
+        try {
+            const url = new URL("{{ route('videos.feed.more') }}", window.location.origin);
+            url.searchParams.set('filter', filter);
+            if (cursor) url.searchParams.set('cursor', cursor);
+            const resp = await fetch(url.toString(), {
+                headers: { 'X-Requested-With': 'XMLHttpRequest', 'Accept': 'application/json' },
+                credentials: 'same-origin',
+            });
+            if (!resp.ok) throw new Error('bad status: ' + resp.status);
+            const data = await resp.json();
+            if (data.items) {
+                grid.insertAdjacentHTML('beforeend', data.items);
+            }
+            cursor = data.next_cursor || '';
+            done   = !data.has_more;
+        } catch (e) {
+            // Reveal the manual Load More so a flaky network doesn't dead-end the user.
+            btnWrap.style.display = 'block';
+        } finally {
+            busy = false;
+            if (done) {
+                btnWrap.style.display = 'none';
+                sentinel.style.display = 'none';
+            }
+        }
+    }
+
+    btn?.addEventListener('click', loadMore);
+
+    if ('IntersectionObserver' in window) {
+        const io = new IntersectionObserver((entries) => {
+            if (entries.some(e => e.isIntersecting)) loadMore();
+        }, { rootMargin: '400px 0px' });
+        io.observe(sentinel);
+    } else {
+        // No IntersectionObserver → surface the Load More fallback immediately.
+        btnWrap.style.display = 'block';
+    }
+})();
 </script>
 @endsection