Reapply "Add missing admin action files and navigation links"

This reverts commit 4d515bc400.

src/components/admin/admin-nav-link.tsx

@@ -9,7 +9,15 @@ import { usePathname } from "next/navigation";
  * exactly; every other entry also matches its sub-routes (e.g. /admin/radio is
  * active on /admin/radio/history) so the current section stays lit.
  */
-export function AdminNavLink({ href, icon, children }: { href: string; icon?: ReactNode; children: ReactNode }) {
+export function AdminNavLink({
+  href,
+  icon,
+  children,
+}: {
+  href: string;
+  icon?: ReactNode;
+  children: ReactNode;
+}) {
   const pathname = usePathname() ?? "";
   const active =
     href === "/admin" ? pathname === "/admin" : pathname === href || pathname.startsWith(`${href}/`);