chore: Update OpenGraph image to Arc logo

Replace default Docusaurus dinosaur with Arc branding.

Author: Ignacio Van Droogenbroeck

docusaurus.config.ts

@@ -53,8 +53,8 @@ const config: Config = {
   ],
 
   themeConfig: {
-    // Replace with your project's social card
-    image: 'img/docusaurus-social-card.jpg',
+    // OpenGraph social card
+    image: 'img/arc.png',
     colorMode: {
       respectPrefersColorScheme: true,
     },