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/read-model.schemas.ts

@@ -1,6 +1,7 @@
 import {
   ActivityReadModel,
   CommentReadModel,
+  NotificationReadModel,
   IssueLinkReadModel,
   IssueReadModel,
   IssueTimelineEntry,
@@ -23,6 +24,11 @@ export type CommentDoc = Doc<CommentReadModel>;
 export type ReleaseDoc = Doc<ReleaseReadModel>;
 export type ActivityDoc = Doc<ActivityReadModel>;
 export type TimelineDoc = Doc<IssueTimelineEntry>;
+export type NotificationDoc = Doc<NotificationReadModel>;
+export interface NotificationSettingsDoc {
+  _id: string;
+  email: boolean;
+}
 
 export const ReadModels = {
   Project: 'ProjectReadModel',
@@ -31,6 +37,8 @@ export const ReadModels = {
   Release: 'ReleaseReadModel',
   Activity: 'ActivityReadModel',
   Timeline: 'IssueTimelineReadModel',
+  Notification: 'NotificationReadModel',
+  NotificationSettings: 'NotificationSettings',
 } as const;
 
 const userRef = { _id: false, id: String, name: String };
@@ -127,6 +135,24 @@ export const TimelineSchema = new Schema<TimelineDoc>(
 );
 TimelineSchema.index({ projectId: 1, at: 1 });
 
+export const NotificationSchema = new Schema<NotificationDoc>(
+  {
+    _id: String,
+    userId: String,
+    readAt: String,
+    createdAt: String,
+    actor: userRef,
+  },
+  { ...loose, collection: 'notifications' },
+);
+NotificationSchema.index({ userId: 1, createdAt: -1 });
+NotificationSchema.index({ userId: 1, readAt: 1 });
+
+export const NotificationSettingsSchema = new Schema<NotificationSettingsDoc>(
+  { _id: String, email: Boolean },
+  { ...loose, collection: 'notification_settings' },
+);
+
 export const READ_MODEL_SCHEMAS = [
   { name: ReadModels.Project, schema: ProjectSchema },
   { name: ReadModels.Issue, schema: IssueSchema },
@@ -134,6 +160,8 @@ export const READ_MODEL_SCHEMAS = [
   { name: ReadModels.Release, schema: ReleaseSchema },
   { name: ReadModels.Activity, schema: ActivitySchema },
   { name: ReadModels.Timeline, schema: TimelineSchema },
+  { name: ReadModels.Notification, schema: NotificationSchema },
+  { name: ReadModels.NotificationSettings, schema: NotificationSettingsSchema },
 ];
 
 export function fromDoc<T extends { _id: string }>(