add favicon; setup opengraph card for homepage

src/app/page.js

···
+import { ImageResponse } from "next/og"
 import styles from "./page.module.css";
+
+export const metadata = {
+  title: process.env.SITENAME,
+  description: process.env.DESCRIPTION, 
+  openGraph: {
+    description: process.env.DESCRIPTION,
+    images: [new ImageResponse(
+      (
+        <div
+          style={{
+            backgroundColor: '#990000',
+            color: '#FFFFFF',
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            width: '100%',
+            height: '100%'
+          }}
+        >
+          {process.env.SITENAME}
+        </div>
+      )
+    )]
+  }
+}
 
 export default function Index() {
   return (