extract metadata merging logic from each page into a helper function

lib/config/metadata.ts

@@ -0,0 +1,47 @@
+import * as config from ".";
+import { BASE_URL } from "./constants";
+import type { Metadata } from "next";
+
+const metadata: Metadata = {
+  metadataBase: new URL(BASE_URL),
+  title: {
+    template: `%s – ${config.siteName}`,
+    default: `${config.siteName} – ${config.shortDescription}`,
+  },
+  description: config.longDescription,
+  openGraph: {
+    siteName: config.siteName,
+    title: {
+      template: "%s",
+      default: `${config.siteName} – ${config.shortDescription}`,
+    },
+    url: "/",
+    locale: config.siteLocale?.replace("-", "_"),
+    type: "website",
+  },
+  twitter: {
+    creator: `@${config.authorSocial?.twitter}`,
+  },
+  alternates: {
+    canonical: "/",
+    types: {
+      "application/rss+xml": [
+        {
+          title: `${config.siteName} (RSS)`,
+          url: "/feed.xml",
+        },
+      ],
+      "application/atom+xml": [
+        {
+          title: `${config.siteName} (Atom)`,
+          url: "/feed.atom",
+        },
+      ],
+    },
+  },
+  other: {
+    humans: "/humans.txt",
+  },
+};
+
+export default metadata;