feat: push selected events to a phone over ntfy

Adds a Notifications tab to Settings so an operator can pick which events
reach their phone, published to a single self-hosted ntfy topic.

The notifier subscribes to the realtime event hub the dashboard already
consumes, so every notifiable event keeps exactly one publisher. Inbound
media had no event, so `media.received` is added and published from the
existing durable `gotImage` gate in the chat service — one notification
per conversation, never repeated when the room re-syncs. It feeds the
in-app notification bell as well.

- Best-effort delivery: a rejecting or unreachable ntfy server is logged
  and never propagated into the path that produced the event.
- Events buffered before the notifier attaches are skipped, so a restart
  cannot replay a backlog to somebody's phone.
- Settings are applied field by field onto the live config object, so a
  save takes effect without a restart.
- The access token is environment-owned (NTFY_AUTH_TOKEN) like the other
  secrets: stripped before the settings record is written, never returned
  by the API, which reports only `hasAuthToken`.

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

apps/dashboard/src/app/notifications.tsx

@@ -77,6 +77,17 @@ export function notificationForEvent(event: DashboardEvent): NotificationDraft |
         tone: 'success',
         href: `/conversations/${encodeURIComponent(event.payload.conversationId)}`,
       };
+    case 'media.received':
+      return {
+        id: event.id,
+        occurredAt: event.occurredAt,
+        title: `Image received from u/${event.payload.sender}`,
+        message: event.payload.count > 1
+          ? `${event.payload.count} images are attached to this conversation.`
+          : 'An image is attached to this conversation.',
+        tone: 'success',
+        href: `/conversations/${encodeURIComponent(event.payload.conversationId)}`,
+      };
     case 'message.sent':
       return {
         id: event.id,