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/issue-created.event-handler.ts

@@ -50,6 +50,7 @@ export class IssueCreatedEventHandler
       assignee: users.ofNullable(issue.assigneeId),
       release: release ? { id: release.id, name: release.name } : null,
       parent: null,
+      sprint: null,
       rank: implicitRank(issue.number),
       labels: issue.labels,
       figmaUrl: issue.figmaUrl,