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/analytics/analytics.spec.ts

@@ -4,10 +4,13 @@ import {
   ReleaseReadModel,
   ReleaseStatus,
   StatusCategory as C,
+  SprintReadModel,
+  SprintStatus,
 } from '@task-stream/api/tracker/domain';
 import {
   computeProjectAnalytics,
   computeReleaseBurnup,
+  computeSprintBurndown,
   weekOf,
 } from './analytics';
 
@@ -182,3 +185,62 @@ describe('release burnup', () => {
     expect(at(burnup.done, '2026-10-14')).toBe(2);
   });
 });
+
+describe('sprint burndown', () => {
+  const sprint = {
+    id: 's1',
+    projectId: 'p',
+    startDate: '2026-10-12',
+    endDate: '2026-10-16',
+    status: SprintStatus.ACTIVE,
+    closedAt: null,
+  } as SprintReadModel;
+  const into = (issueId: string, at: string): IssueTimelineEntry => ({
+    id: `${issueId}:${++seq}`,
+    issueId,
+    projectId: 'p',
+    at,
+    kind: 'sprint',
+    sprintId: 's1',
+  });
+  // X (3 points) and Y (5) committed on Monday; Z (2) added on Tuesday.
+  // X done on Tuesday, Y cancelled on Wednesday. Today is Wednesday noon.
+  const issues = [
+    { ...issue('x', '2026-10-01T09:00:00Z', 'DONE', C.DONE), storyPoints: 3 },
+    {
+      ...issue('y', '2026-10-01T09:00:00Z', 'CANCELLED', C.CANCELLED),
+      storyPoints: 5,
+    },
+    { ...issue('z', '2026-10-01T09:00:00Z', 'TODO', C.TODO), storyPoints: 2 },
+  ] as IssueReadModel[];
+  const timeline = [
+    step('x', '2026-10-01T09:00:00Z', 'TODO', C.TODO),
+    step('y', '2026-10-01T09:00:00Z', 'TODO', C.TODO),
+    step('z', '2026-10-01T09:00:00Z', 'TODO', C.TODO),
+    into('x', '2026-10-12T08:00:00Z'),
+    into('y', '2026-10-12T08:00:00Z'),
+    into('z', '2026-10-13T10:00:00Z'),
+    step('x', '2026-10-13T16:00:00Z', 'DONE', C.DONE),
+    step('y', '2026-10-14T09:00:00Z', 'CANCELLED', C.CANCELLED),
+  ];
+
+  it('counts open tickets and points per day, and leaves the future blank', () => {
+    const burndown = computeSprintBurndown({
+      sprint,
+      issues,
+      timeline,
+      now: new Date('2026-10-14T12:00:00Z'),
+    });
+    expect(burndown.dates).toEqual([
+      '2026-10-12',
+      '2026-10-13',
+      '2026-10-14',
+      '2026-10-15',
+      '2026-10-16',
+    ]);
+    expect(burndown.scope).toEqual([2, 3, 2, null, null]);
+    expect(burndown.remaining).toEqual([2, 2, 1, null, null]);
+    expect(burndown.remainingPoints).toEqual([8, 7, 2, null, null]);
+    expect(burndown.ideal).toEqual([2, 1.5, 1, 0.5, 0]);
+  });
+});