feat(frontend): add /u/[user]

frontend/components/BlueLink.tsx

@@ -0,0 +1,14 @@
+import Link from "next/link";
+
+export type Props = {
+  to: string;
+  children?: React.ReactNode;
+};
+
+export default function BlueLink({ to, children }: Props) {
+  return (
+    <Link href={to} className="hover:underline text-sky-500 dark:text-sky-400">
+      {children}
+    </Link>
+  );
+}