feat: add SiteFooter component and integrate it into RootLayout

components/site-footer.tsx

@@ -0,0 +1,17 @@
+export function SiteFooter() {
+  return (
+    <footer className="border-t bg-card/60">
+      <div className="mx-auto flex w-full max-w-6xl items-center justify-center px-4 py-4 text-center text-xs text-muted-foreground sm:px-8 sm:text-sm">
+        運用元:
+        <a
+          href="https://neody.land/ja"
+          target="_blank"
+          rel="noopener noreferrer"
+          className="ml-1 font-medium text-foreground underline underline-offset-4 hover:text-primary"
+        >
+          Neodyland
+        </a>
+      </div>
+    </footer>
+  );
+}