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>

apps/web/src/app/app.routes.spec.ts

@@ -29,6 +29,7 @@ describe('appRoutes', () => {
       'board',
       'issues/:issueKey',
       'backlog',
+      'sprints',
       'epics',
       'releases',
       'dashboard',