Reapply "Add missing admin action files and navigation links"

This reverts commit 4d515bc400.

src/app/u/[username]/page.tsx

@@ -40,11 +40,7 @@ function formatDate(d: Date | null | undefined): string {
   return d ? d.toISOString().slice(0, 10) : "";
 }
 
-export default async function ProfilePage({
-  params,
-}: {
-  params: Promise<{ username: string }>;
-}) {
+export default async function ProfilePage({ params }: { params: Promise<{ username: string }> }) {
   const t = await getTranslations("pages.profile");
   const { username } = await params;
 
@@ -83,10 +79,8 @@ export default async function ProfilePage({
       select: { type: true, amount: true },
     })
     .catch(() => []);
-  const ducketsAmount =
-    currencyRows.find((c) => c.type === CURRENCY_DUCKETS)?.amount ?? 0;
-  const diamondsAmount =
-    currencyRows.find((c) => c.type === CURRENCY_DIAMONDS)?.amount ?? 0;
+  const ducketsAmount = currencyRows.find((c) => c.type === CURRENCY_DUCKETS)?.amount ?? 0;
+  const diamondsAmount = currencyRows.find((c) => c.type === CURRENCY_DIAMONDS)?.amount ?? 0;
   const wallet = [
     {
       key: "credits",
@@ -412,7 +406,11 @@ export default async function ProfilePage({
       </ContentCard>
 
       {/* ── Guestbook ───────────────────── */}
-      <ContentCard icon="📝" title={t("guestbookTitle")} subtitle={t("guestbookSubtitle", { username: user.username })}>
+      <ContentCard
+        icon="📝"
+        title={t("guestbookTitle")}
+        subtitle={t("guestbookSubtitle", { username: user.username })}
+      >
         {isLoggedIn ? (
           <form action={postGuestbook} className="card" style={{ marginBottom: "1rem" }}>
             {/* Profile owner id drives the write target; the author is taken from