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>

packages/api-contracts/src/events.ts

@@ -83,6 +83,15 @@ export const DashboardEventSchema = z.discriminatedUnion('type', [
       preview: z.string().optional(),
     }),
   }),
+  z.strictObject({
+    ...EventBase,
+    type: z.literal('media.received'),
+    payload: z.strictObject({
+      conversationId: z.string(),
+      sender: z.string(),
+      count: z.number(),
+    }),
+  }),
   z.strictObject({
     ...EventBase,
     type: z.literal('sync.started'),