feat: notifications in the app and, optionally, by e-mail

Derived from events and kept per person: whoever a ticket is assigned to,
whoever reports or works on it when it moves, fails QA or gets a comment,
and whoever joins a project. Never about what you did yourself, once per
event. They arrive live through a subscription to a bell in the header,
and are copied by e-mail to whoever turns it on when SMTP_URL is set.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/application/src/lib/events/inbox.events.ts

@@ -0,0 +1,37 @@
+import { type } from '@ngrx/signals';
+import { eventGroup } from '@ngrx/signals/events';
+import {
+  Notification,
+  NotificationSettings,
+} from '@task-stream/web/tracker/domain';
+
+/* Notifications are "the inbox" here, so as not to clash with `Notifications` (the toasts port). */
+
+export const inboxPageEvents = eventGroup({
+  source: 'Inbox',
+  events: {
+    /** Signed in: load, and follow new ones. */
+    opened: type<void>(),
+    /** Signed out: forget everything. */
+    closed: type<void>(),
+    markReadRequested: type<{ ids?: string[] }>(),
+    emailToggled: type<boolean>(),
+  },
+});
+
+export const inboxApiEvents = eventGroup({
+  source: 'Inbox API',
+  events: {
+    loaded: type<{ items: Notification[]; unread: number }>(),
+    settingsLoaded: type<NotificationSettings>(),
+    markedRead: type<{ ids?: string[]; at: string }>(),
+    failed: type<string>(),
+  },
+});
+
+export const inboxRealtimeEvents = eventGroup({
+  source: 'Inbox Realtime',
+  events: {
+    arrived: type<Notification>(),
+  },
+});