Change pagination to 21 per page

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: danlex

index.html

@@ -4798,7 +4798,7 @@ <h1>GPU Particle Animations</h1>
     // ==========================================
     // PAGINATION + FILTERING
     // ==========================================
-    const PER_PAGE = 20;
+    const PER_PAGE = 21;
     const urlParams = new URLSearchParams(window.location.search);
     let currentPage = parseInt(urlParams.get('page')) || 1;
     let currentFilter = urlParams.get('filter') || 'all';