feat(db): add pure isBanActive predicate matching Laravel ban filtering

packages/db/src/bans/is-ban-active.ts

@@ -0,0 +1,5 @@
+// Mirrors Laravel's active-ban query: where('ban_expire', '>', time()).
+// ban_expire and now are both unix timestamps in seconds.
+export function isBanActive(ban: { banExpire: number }, nowUnixSeconds: number): boolean {
+  return ban.banExpire > nowUnixSeconds;
+}