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/mongo/notifications.repository.ts

@@ -0,0 +1,73 @@
+import { Injectable } from '@nestjs/common';
+import { InjectModel } from '@nestjs/mongoose';
+import { NotificationsRepository } from '@task-stream/api/tracker/application';
+import {
+  NotificationReadModel,
+  NotificationSettingsReadModel,
+} from '@task-stream/api/tracker/domain';
+import { Model } from 'mongoose';
+import {
+  fromDoc,
+  NotificationDoc,
+  NotificationSettingsDoc,
+  ReadModels,
+} from './read-model.schemas';
+
+@Injectable()
+export class MongoNotificationsRepository extends NotificationsRepository {
+  constructor(
+    @InjectModel(ReadModels.Notification)
+    private readonly notifications: Model<NotificationDoc>,
+    @InjectModel(ReadModels.NotificationSettings)
+    private readonly settingsDocs: Model<NotificationSettingsDoc>,
+  ) {
+    super();
+  }
+
+  async insert({ id, ...rest }: NotificationReadModel): Promise<boolean> {
+    const result = await this.notifications.updateOne(
+      { _id: id },
+      { $setOnInsert: rest },
+      { upsert: true },
+    );
+    return result.upsertedCount > 0;
+  }
+
+  async findForUser(
+    userId: string,
+    options: { unreadOnly: boolean; limit: number },
+  ): Promise<NotificationReadModel[]> {
+    const docs = await this.notifications
+      .find({ userId, ...(options.unreadOnly ? { readAt: null } : {}) })
+      .sort({ createdAt: -1 })
+      .limit(options.limit)
+      .lean<NotificationDoc[]>();
+    return docs.map((doc) => fromDoc(doc) as NotificationReadModel);
+  }
+
+  countUnread(userId: string): Promise<number> {
+    return this.notifications.countDocuments({ userId, readAt: null });
+  }
+
+  async markRead(userId: string, ids: string[] | null): Promise<void> {
+    await this.notifications.updateMany(
+      { userId, readAt: null, ...(ids ? { _id: { $in: ids } } : {}) },
+      { $set: { readAt: new Date().toISOString() } },
+    );
+  }
+
+  async settings(userId: string): Promise<NotificationSettingsReadModel> {
+    const doc = await this.settingsDocs
+      .findById(userId)
+      .lean<NotificationSettingsDoc>();
+    return { userId, email: doc?.email ?? false };
+  }
+
+  async saveSettings(settings: NotificationSettingsReadModel): Promise<void> {
+    await this.settingsDocs.updateOne(
+      { _id: settings.userId },
+      { $set: { email: settings.email } },
+      { upsert: true },
+    );
+  }
+}