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/features/settings/settings-route.tsx

@@ -1,7 +1,7 @@
 import { useSearchParams } from 'react-router-dom';
 import { SettingsPage, type SettingsSection } from './settings-page.js';
 
-const validSections: readonly SettingsSection[] = ['monitoring', 'rate-limits', 'behaviour', 'access'];
+const validSections: readonly SettingsSection[] = ['monitoring', 'rate-limits', 'behaviour', 'notifications', 'access'];
 
 function parseSection(value: string | null): SettingsSection {
   return validSections.find((section) => section === value) ?? 'monitoring';