refactor: centralize duplicated formatDate helper

21 files defined their own local formatDate (with three different output
formats: date, datetime, datetime-seconds, and varying null fallbacks).
Replace them with a single shared helper at src/lib/format-date.ts that
takes a variant + optional fallback, preserving the exact previous output
per call site (verified identical string results).

Removes ~21 copies of the same logic. photos.tsx and media-grid.tsx keep
their epoch-ms based formatters since those are a different input shape.

Verified: tsc --noEmit clean, full test suite green (301/301).

src/app/admin/ip/page.tsx

@@ -1,4 +1,5 @@
 import { getTranslations } from "next-intl/server";
+import { formatDate } from "@/lib/format-date";
 import {
 	addBlacklist,
 	addWhitelist,
@@ -19,9 +20,6 @@ type IpRow = {
 	createdAt: Date | null;
 };
 
-function formatDate(d: Date | null): string {
-	return d ? d.toISOString().slice(0, 16).replace("T", " ") : "—";
-}
 
 export default async function AdminIp() {
 	const { session, permissions } = await getAdminContext();
@@ -113,7 +111,7 @@ export default async function AdminIp() {
 												{w.asn ?? "—"}
 											</td>
 											<td className="text-sm theme-text-muted dark:theme-text-muted whitespace-nowrap">
-												{formatDate(w.createdAt)}
+												{formatDate(w.createdAt, "datetime", "—")}
 											</td>
 											<td>
 												<form action={deleteWhitelist}>
@@ -175,7 +173,7 @@ export default async function AdminIp() {
 												{b.asn ?? "—"}
 											</td>
 											<td className="text-sm theme-text-muted dark:theme-text-muted whitespace-nowrap">
-												{formatDate(b.createdAt)}
+												{formatDate(b.createdAt, "datetime", "—")}
 											</td>
 											<td>
 												<form action={deleteBlacklist}>