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/puzzle.php

@@ -0,0 +1,29 @@
+
+<div class="container mx-auto py-8">
+  <h2>Training & Lichess TV</h2>
+  <div class="grid grid-cols-1 lg:grid-cols-2 gap-6 w-full">
+    <!-- Erste Spalte - Lichess Training -->
+    <div class="w-full flex flex-col items-center">
+      <h3 class="text-lg font-semibold mb-3 text-gray-800">Tägliches Rätsel</h3>
+      <iframe 
+        src="https://lichess.org/training/frame?theme=blue&bg=light&pieceSet=staunty" 
+        style="width:400px; aspect-ratio: 10/11;"
+        allowtransparency="true" 
+        frameborder="0"
+        scrolling="no">
+      </iframe>
+    </div>
+    
+    <!-- Zweite Spalte - Lichess Puzzle -->
+    <div class="w-full flex flex-col items-center">
+      <h3 class="text-lg font-semibold mb-3 text-gray-800">Lichess TV</h3>
+      <iframe 
+        src="https://lichess.org/tv/frame?theme=blue&bg=light&pieceSet=staunty" 
+        style="width:390px; aspect-ratio: 10/11"
+        allowtransparency="true" 
+        frameborder="0"
+        scrolling="no">
+      </iframe>
+    </div>
+  </div>
+</div>