feat: add font integration and update layout for additional stylesheets

Integrated new fonts (Ubuntu and Roboto) with `@font-face`, added `fonts.css` for font definitions. Updated layout snippet to include `pgn4web.css` and `fonts.css` for extended styling support.

assets/css/fonts.css

@@ -0,0 +1,33 @@
+/* ubuntu-300 - latin */
+@font-face {
+    font-display: swap; /* Check https://developer.mozilla.org/en-US/docs/Web/CSS/@font-face/font-display for other options. */
+    font-family: 'Ubuntu';
+    font-style: normal;
+    font-weight: 300;
+    src: url('../fonts/ubuntu-v20-latin-300.woff2') format('woff2'); /* Chrome 36+, Opera 23+, Firefox 39+, Safari 12+, iOS 10+ */
+}
+/* ubuntu-regular - latin */
+@font-face {
+    font-display: swap; /* Check https://developer.mozilla.org/en-US/docs/Web/CSS/@font-face/font-display for other options. */
+    font-family: 'Ubuntu';
+    font-style: normal;
+    font-weight: 400;
+    src: url('../fonts/ubuntu-v20-latin-regular.woff2') format('woff2'); /* Chrome 36+, Opera 23+, Firefox 39+, Safari 12+, iOS 10+ */
+}
+/* ubuntu-700 - latin */
+@font-face {
+    font-display: swap; /* Check https://developer.mozilla.org/en-US/docs/Web/CSS/@font-face/font-display for other options. */
+    font-family: 'Ubuntu';
+    font-style: normal;
+    font-weight: 700;
+    src: url('../fonts/ubuntu-v20-latin-700.woff2') format('woff2'); /* Chrome 36+, Opera 23+, Firefox 39+, Safari 12+, iOS 10+ */
+}
+
+/* roboto-regular - latin */
+@font-face {
+    font-display: swap; /* Check https://developer.mozilla.org/en-US/docs/Web/CSS/@font-face/font-display for other options. */
+    font-family: 'Roboto';
+    font-style: normal;
+    font-weight: 400;
+    src: url('../fonts/roboto-v48-latin-regular.woff2') format('woff2'); /* Chrome 36+, Opera 23+, Firefox 39+, Safari 12+, iOS 10+ */
+}

site/snippets/layout.php

@@ -8,7 +8,9 @@
 
         <?= css([
             'assets/css/styles.css',
-            'assets/css/chess.css'
+            'assets/css/chess.css',
+            'assets/css/pgn4web.css',
+            'assets/css/fonts.css',
         ]) ?>
 
         <?= js([