feat(channel): /@handle/{tab} aliases + cursor pagination on Videos tab

Two complementary additions that share the same bridge-not-rewrite
philosophy — reuse the existing single-page channel view instead of
splitting its 2000 lines into five route-driven partials.

/@handle/{tab}: videos / shorts / playlists / posts / about / wall
redirect to the equivalent /channel/{slug}#tab URL (302). The channel
page's existing hash-tab JS already handles landing on the right tab;
these aliases just make the URLs shareable in the YouTube style.

Channel Videos tab Load More: new JSON endpoint
GET /channel/{username}/videos/more returns the next cursor page of
server-rendered video cards. A sentinel + IntersectionObserver below
the grid fetches the next page when scrolled into view, with a Load
More button as fallback. Behavior mirrors the Phase 2 home feed —
users with thousands of uploads no longer get a 300-item grid on
first paint.

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

app/Http/Controllers/UserController.php

@@ -18,7 +18,7 @@ class UserController extends Controller
 {
     public function __construct()
     {
-        $this->middleware('auth')->except(['channel']);
+        $this->middleware('auth')->except(['channel', 'channelVideosMore']);
     }
 
     // Typeahead search for members (used by the "Share to member" picker)
@@ -372,6 +372,38 @@ class UserController extends Controller
         return redirect()->route('history')->with('toast_success', 'Watch history cleared.');
     }
 
+    /**
+     * JSON endpoint powering the "Load more" button on the channel Videos
+     * tab. Takes a username + optional cursor and returns a page of
+     * server-rendered video cards + next cursor. Reuses the cursorPaginate
+     * pattern Phase 2 established for the home feed.
+     */
+    public function channelVideosMore(Request $request, string $username)
+    {
+        $owner  = User::where('username', $username)->firstOrFail();
+        $viewer = Auth::user();
+        $isOwner = $viewer && $viewer->id === $owner->id;
+
+        $query = $isOwner
+            ? Video::where('user_id', $owner->id)
+            : Video::public()->where('user_id', $owner->id);
+
+        $paginator = $query->where('is_shorts', false)
+            ->latest('id')
+            ->cursorPaginate(24);
+
+        $html = '';
+        foreach ($paginator->items() as $video) {
+            $html .= view('components.video-card', ['video' => $video, 'hideChannelInfo' => true])->render();
+        }
+
+        return response()->json([
+            'items'       => $html,
+            'next_cursor' => optional($paginator->nextCursor())->encode(),
+            'has_more'    => $paginator->hasMorePages(),
+        ]);
+    }
+
     /**
      * Subscriptions feed — the public videos uploaded by every channel the
      * viewer is subscribed to, newest first. Replaces the dead href="#" that