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/presenters/src/lib/graphql/subscription.resolver.ts

@@ -12,6 +12,7 @@ import {
   NotificationGql,
   ProjectChangeGql,
   ReleaseChangeGql,
+  SprintChangeGql,
 } from './types';
 
 const asIs = { resolve: <T>(payload: T) => payload };
@@ -66,6 +67,14 @@ export class SubscriptionResolver {
     return this.changes.watchReleases(me.id, projectId);
   }
 
+  @Subscription(() => SprintChangeGql, asIs)
+  sprintChanged(
+    @CurrentUser() me: User,
+    @Args('projectId', { type: () => ID }) projectId: string,
+  ) {
+    return this.changes.watchSprints(me.id, projectId);
+  }
+
   @Subscription(() => ProjectChangeGql, asIs)
   projectChanged(
     @CurrentUser() me: User,