Add registration status badges and auto-dismissing dashboard messages

Two consistency fixes requested after the payment-method work:

1. Registration status (pending/confirmed/partial_paid/paid/cancelled)
   was printed as a raw string on the user dashboard. Added
   RegistrationStatusBadge mirroring the existing EventStatusBadge
   pattern, using the same status colors already established on
   dashboard/admin/registrations.

2. Inline success/error banners across dashboard pages persisted
   indefinitely. Added a shared useDismissingState hook (drop-in
   useState replacement that auto-clears a truthy value after 7s,
   resetting the timer on each update) and swapped it in across ~24
   dashboard files. Excluded: message-only modal dialogs (ticket-
   scanning's success/error confirmations) and two states that mix
   live form-validation feedback with async results inside actively-
   open forms (the registration-edit modal's editError, the event
   create/edit modal's error) - those keep persisting until the user
   acts, since auto-hiding a "fix this field" message mid-edit would
   be a regression. Also fixed at-the-door's existing bespoke
   auto-dismiss timers (10s/15s, one mislabeled as "5s") to the same
   consistent 7s, and removed admin/settings' manual x dismiss button
   in favor of the same auto-only behavior.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/app/dashboard/supervisor/events/page.tsx

@@ -5,6 +5,7 @@ import { createPortal } from "react-dom";
 import { useAuth } from "@/hooks/useAuth";
 import { useRouter } from "next/navigation";
 import { apiFetch, resolveToApiOrigin } from "@/lib/api";
+import { useDismissingState } from "@/hooks/useDismissingState";
 
 // ─── helpers ────────────────────────────────────────────────────────────────
 
@@ -690,7 +691,7 @@ function NotifyRecipientsManager({ eventId, creator, initialRecipients }: { even
   const [selected, setSelected] = useState<NotifyUser[]>(initialRecipients || []);
   const [loading, setLoading] = useState(!hasInitial);
   const [saving, setSaving] = useState(false);
-  const [error, setError] = useState<string | null>(null);
+  const [error, setError] = useDismissingState<string | null>(null);
 
   useEffect(() => {
     if (hasInitial) return; // already have the data — skip the network round trip entirely
@@ -1415,7 +1416,7 @@ export default function ManageEventsPage() {
 
   const [events, setEvents] = useState<any[]>([]);
   const [loadingEvents, setLoadingEvents] = useState(false);
-  const [error, setError] = useState<string | null>(null);
+  const [error, setError] = useDismissingState<string | null>(null);
 
   const loadEvents = async () => {
     if (!token) return;