fix: Fix corner logo transparency (#48)

Fix corner logo lack of transparency.

Also use a more standard format (PNG - which also supports transparency
to begin with), and a better name (follow `-` name convention).


![image](https://github.com/flame-engine/flame-engine-site/assets/882703/013d3f66-a324-4775-b482-ede25eb339cc)

_includes/nav.html

@@ -1,7 +1,7 @@
 <nav class="h-16 md:h-32 flex items-center justify-between">
     <div class="flex-initial items-center collapse md:visible">
         <a href="/">
-            <img src="assets/images/cornerlogo.jpg"/>
+            <img src="assets/images/corner-logo.png" />
         </a>
     </div>
     <div class="flex flex-wrap items-center justify-center justify-items-center text-text font-extrabold space-x-8">