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/domain/src/index.ts

@@ -11,6 +11,8 @@ export * from './lib/project/project-settings';
 export * from './lib/comment/comment';
 export * from './lib/release/release';
 export * from './lib/release/release-status';
+export * from './lib/sprint/sprint';
+export * from './lib/sprint/sprint-status';
 export * from './lib/events';
 export * from './lib/factories';
 export * from './lib/read-models';