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/presenters/src/lib/http/dto/responses.dto.ts

@@ -2,6 +2,7 @@ import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
 import {
   IssueLinkType,
   IssuePriority,
+  NotificationKind,
   ProjectRole,
   ReleaseStatus,
   SETTING_COLORS,
@@ -354,3 +355,40 @@ export class ReleaseBurnupDto {
   scope!: number[];
   @ApiProperty({ type: [Number] }) done!: number[];
 }
+
+// ---- Notifications ----------------------------------------------------------
+
+export class NotificationDto {
+  @ApiProperty() id!: string;
+  @ApiProperty({ enum: NotificationKind, enumName: 'NotificationKind' })
+  kind!: NotificationKind;
+  @ApiProperty({ format: 'uuid' }) projectId!: string;
+  @ApiProperty({ example: 'WEB' }) projectKey!: string;
+  @ApiProperty({ type: String, nullable: true, format: 'uuid' })
+  issueId!: string | null;
+  @ApiProperty({ type: String, nullable: true, example: 'WEB-12' })
+  issueKey!: string | null;
+  @ApiProperty({ type: UserRefDto }) actor!: UserRefDto;
+  @ApiProperty({ example: 'Ana te asignó WEB-12: Login roto en Safari' })
+  summary!: string;
+  @ApiProperty({
+    type: String,
+    nullable: true,
+    format: 'date-time',
+    description: 'Null: unread',
+  })
+  readAt!: string | null;
+  @ApiProperty({ format: 'date-time' }) createdAt!: string;
+}
+
+export class MyNotificationsDto {
+  @ApiProperty({ type: [NotificationDto] }) items!: NotificationDto[];
+  @ApiProperty({ description: 'All my unread ones, not just these' })
+  unread!: number;
+}
+
+export class NotificationSettingsResponseDto {
+  @ApiProperty({ description: 'Copies by e-mail' }) email!: boolean;
+  @ApiProperty({ description: 'Whether this installation can send e-mail' })
+  emailAvailable!: boolean;
+}