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/hero.php

@@ -49,7 +49,7 @@
             <!-- Rechte Spalte - GIF -->
             <div class="w-3/4 md:w-1/2">
                 <div class="rounded-lg overflow-hidden shadow-xl">
-                    <img src="/assets/img/Hort-Martius-2.gif"
+                    <img src="/assets/img/Hort-Martius.gif"
                          alt="Animation"
                          class="w-full h-auto">
                 </div>