feat: add FEN block support and related assets

Introduced a new FEN block feature, including a PHP snippet to render FEN diagrams, a new CSS file for chessboard styling, font integration, and blueprint updates. Adjusted asset paths and file references for consistency.

site/snippets/layout.php

@@ -8,7 +8,7 @@
 
         <?= css([
             'assets/css/styles.css',
-            'assets/css/png4web.css',
+            'assets/css/chess.css'
         ]) ?>
 
         <link rel="shortcut icon" type="image/x-icon"
@@ -40,6 +40,8 @@
         <footer class="bg-sf_grau-400 w-full" id="footer">
             <?php snippet('footer') ?>
         </footer>
-        <?= js('assets/js/navbar.js') ?>
+        <?= js([
+                'assets/js/navbar.js'
+        ]) ?>
     </body>
 </html>