fix(og-images): wrap Buffer in Uint8Array for Response body (#568)

Astro uses Web API typings; Response doesn’t accept Node Buffer. Convert
the generated OG image Buffer to Uint8Array before constructing Response
to satisfy BodyInit and fix the build/type error.

Closes #560

src/pages/og.png.ts

@@ -1,7 +1,9 @@
 import type { APIRoute } from "astro";
 import { generateOgImageForSite } from "@/utils/generateOgImages";
 
-export const GET: APIRoute = async () =>
-  new Response(await generateOgImageForSite(), {
+export const GET: APIRoute = async () => {
+  const buffer = await generateOgImageForSite();
+  return new Response(new Uint8Array(buffer), {
     headers: { "Content-Type": "image/png" },
   });
+};