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/api/tracker/infrastructure/src/lib/tracker-infrastructure.module.ts

@@ -5,6 +5,8 @@ import { TypeOrmModule } from '@nestjs/typeorm';
 import {
   AttachmentStorage,
   ChangeFeed,
+  NotificationMailer,
+  NotificationsRepository,
   FindActivityRepository,
   FindCommentsRepository,
   FindIssuesRepository,
@@ -52,6 +54,8 @@ import {
 import { PostgresReleaseIssuesRepository } from './postgres/release-issues.repository';
 import { PostgresTrackerStreamsRepository } from './postgres/tracker-streams.repository';
 import { RedisChangeFeed } from './realtime/redis-change-feed';
+import { MongoNotificationsRepository } from './mongo/notifications.repository';
+import { SmtpNotificationMailer } from './mail/smtp-notification.mailer';
 import { FileSystemAttachmentStorage } from './storage/file-system-attachment.storage';
 
 const PORTS = [
@@ -100,6 +104,9 @@ const PORTS = [
   },
   // Attached files → disk (ATTACHMENTS_DIR)
   { provide: AttachmentStorage, useClass: FileSystemAttachmentStorage },
+  // Notifications → MongoDB (per person), copies by e-mail → SMTP (optional)
+  { provide: NotificationsRepository, useClass: MongoNotificationsRepository },
+  { provide: NotificationMailer, useClass: SmtpNotificationMailer },
   // Realtime → Redis pub/sub
   { provide: ChangeFeed, useClass: RedisChangeFeed },
   // Identity context (anti-corruption layer)