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/testing/in-memory.ts

@@ -243,6 +243,20 @@ export class InMemoryTrackerStreams extends TrackerStreamsRepository {
     );
   }
 
+  async sprintIdsOfProject(projectId: string) {
+    return this.streams(
+      'SprintCreatedEvent',
+      (d) => d['projectId'] === projectId,
+    );
+  }
+
+  async issueIdsEverInSprint(sprintId: string) {
+    return this.streams(
+      'IssueSprintChangedEvent',
+      (d) => d['sprintId'] === sprintId,
+    );
+  }
+
   async commentIdsOfIssue(issueId: string) {
     return this.streams(
       'CommentAddedEvent',