Adds chess analysis page

Adds a new page for chess analysis, powered by lichess.org,
and integrates it into the navigation menu. Also adds daily
puzzle snippet to home page. Updates hero image to correct gif.

site/snippets/analyse.php

@@ -0,0 +1,9 @@
+  <h2>Schachanalyse</h2>
+  <p>powered by lichess.org</p>
+  <div class="w-full flex justify-center mt-4">
+    <iframe 
+      src="https://lichess.org/embed/analysis?theme=blue&bg=light&pieceSet=staunty" 
+      style="width: 100%; aspect-ratio: 4/4;" 
+      frameborder="0">
+    </iframe>
+  </div>