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/domain/src/lib/ports/gateways.ts

@@ -8,6 +8,8 @@ import {
   Issue,
   IssuePage,
   IssueSummary,
+  Notification,
+  NotificationSettings,
   Project,
   ProjectAnalytics,
   ProjectStats,
@@ -130,6 +132,18 @@ export abstract class UsersGateway {
   abstract search(term: string): Observable<UserDirectoryEntry[]>;
 }
 
+/** The signed-in person's notifications. */
+export abstract class NotificationsGateway {
+  abstract mine(
+    unreadOnly: boolean,
+    limit: number,
+  ): Observable<{ items: Notification[]; unread: number }>;
+  /** Without ids: all of them. */
+  abstract markRead(ids?: string[]): Observable<void>;
+  abstract settings(): Observable<NotificationSettings>;
+  abstract updateSettings(email: boolean): Observable<NotificationSettings>;
+}
+
 /** Realtime (GraphQL subscriptions over WebSocket). */
 export interface IssueChanged {
   action: string;
@@ -158,4 +172,5 @@ export abstract class TrackerRealtimeGateway {
   abstract releaseChanges(projectId: string): Observable<Release>;
   abstract projectChanges(projectId: string): Observable<ProjectChanged>;
   abstract myProjectsChanges(): Observable<ProjectChanged>;
+  abstract notifications(): Observable<Notification>;
 }