Add Knights interactive to index

Add the Knights interactive to the index page.

src/pages/Index.tsx

@@ -55,6 +55,13 @@ const featuredInteractives = [{
   tags: ['strategy', 'board-game', 'two-player'],
   path: '/northcotts-game',
   theme: 'Games'
+}, {
+  id: 'knights-puzzle',
+  title: 'Knights Exchange Puzzle',
+  description: 'A classic chess puzzle where you must exchange the positions of white and black knights using legal knight moves.',
+  tags: ['chess', 'knights', 'puzzle'],
+  path: '/knights-puzzle',
+  theme: 'Puzzles'
 }];
 const Index = () => {
   return <Layout>