Refresh desktop screenshots across the website and README

site/index.html

@@ -63,11 +63,11 @@
       </section>
       <figure class="product-screenshot page-width">
         <a
-          href="assets/ferese-desktop.png"
+          href="assets/ferese-desktop.webp"
           aria-label="View the full-resolution Ferese desktop screenshot"
         >
           <img
-            src="assets/ferese-desktop.png"
+            src="assets/ferese-desktop.webp"
             width="2880"
             height="1800"
             alt="Ferese Blue desktop with the default wallpaper, Settings, Control Center and clock widget"