feat: sprints with burndown and carry-over

Plan sprints with dates and a goal, run one at a time per project, and
put tickets in them from the ticket page. The Sprints tab follows the one
under way with its progress and a burndown in tickets or points against
the ideal line. Closing a sprint sends what was left to the next one or
back to the backlog; the board can be filtered by sprint.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/api/tracker/application/src/lib/event-handlers/sprint.event-handler.ts

@@ -0,0 +1,65 @@
+import { EventsHandler, IEventHandler } from '@nestjs/cqrs';
+import {
+  SprintClosedEvent,
+  SprintCreatedEvent,
+  SprintDeletedEvent,
+  SprintStartedEvent,
+  SprintStatus,
+  SprintUpdatedEvent,
+} from '@task-stream/api/tracker/domain';
+import { UpsertMaterializedIssueRepository } from '../ports/upsert-materialized-issue.repository';
+import { UpsertMaterializedSprintRepository } from '../ports/upsert-materialized-sprint.repository';
+import { ReadModelNotifier, versionOf } from './read-model-notifier';
+
+type SprintEvent =
+  | SprintCreatedEvent
+  | SprintUpdatedEvent
+  | SprintStartedEvent
+  | SprintClosedEvent
+  | SprintDeletedEvent;
+
+/** The sprints view (`sprints_view`), one document per sprint. */
+@EventsHandler(
+  SprintCreatedEvent,
+  SprintUpdatedEvent,
+  SprintStartedEvent,
+  SprintClosedEvent,
+  SprintDeletedEvent,
+)
+export class SprintEventHandler implements IEventHandler<SprintEvent> {
+  constructor(
+    private readonly sprints: UpsertMaterializedSprintRepository,
+    private readonly issues: UpsertMaterializedIssueRepository,
+    private readonly notifier: ReadModelNotifier,
+  ) {}
+
+  async handle(event: SprintEvent) {
+    const version = versionOf(event);
+    const id = event.aggregateId;
+    if (event instanceof SprintCreatedEvent) {
+      await this.sprints.upsert({ ...event.sprint, version });
+    } else if (event instanceof SprintUpdatedEvent) {
+      await this.sprints.upsert({ id, ...event.changes, version });
+      // Tickets show its name.
+      if (event.changes.name)
+        await this.issues.renameSprint(id, event.changes.name);
+    } else if (event instanceof SprintStartedEvent) {
+      await this.sprints.upsert({
+        id,
+        status: SprintStatus.ACTIVE,
+        startedAt: event.occurredAt,
+        version,
+      });
+    } else if (event instanceof SprintClosedEvent) {
+      await this.sprints.upsert({
+        id,
+        status: SprintStatus.CLOSED,
+        closedAt: event.occurredAt,
+        version,
+      });
+    } else {
+      await this.sprints.remove(id);
+    }
+    await this.notifier.sprint(id, event);
+  }
+}