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/radio/page.tsx

@@ -1,4 +1,5 @@
 import { getTranslations } from "next-intl/server";
+import { formatDate } from "@/lib/format-date";
 import { deleteShout } from "@/actions/admin-radio-moderation";
 import { StatusCard } from "@/components/admin/dashboard";
 import { prisma } from "@/lib/prisma";
@@ -33,9 +34,6 @@ type Schedule = {
 	isActive: boolean;
 };
 
-function formatDate(d: Date | null): string {
-	return d ? d.toISOString().slice(0, 16).replace("T", " ") : "\u2014";
-}
 
 function formatTime(d: Date | null): string {
 	return d ? d.toISOString().slice(11, 16) : "\u2014";
@@ -162,7 +160,7 @@ export default async function AdminRadioPage() {
 									<td>{String(s.userId)}</td>
 									<td>{s.message}</td>
 									<td className="text-sm theme-text-muted dark:theme-text-muted">
-										{formatDate(s.createdAt)}
+										{formatDate(s.createdAt, "datetime", "\u2014")}
 									</td>
 									<td>
 										<form action={deleteShout}>
@@ -218,7 +216,7 @@ export default async function AdminRadioPage() {
 										</span>
 									</td>
 									<td className="text-sm theme-text-muted dark:theme-text-muted">
-										{formatDate(a.createdAt)}
+										{formatDate(a.createdAt, "datetime", "\u2014")}
 									</td>
 								</tr>
 							))}