feat: an ordered backlog

A Backlog tab lists the tickets still to start in the order the team will
take them; drag them, or use the arrows, to reorder. Moving a ticket only
rewrites that ticket's rank, read from the event store, and board columns
follow the same order.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/api/tracker/application/src/lib/event-handlers/issue-created.event-handler.ts

@@ -2,6 +2,7 @@ import { EventsHandler, IEventHandler } from '@nestjs/cqrs';
 import {
   DEFAULT_PROJECT_SETTINGS,
   IssueCreatedEvent,
+  implicitRank,
   ProjectWorkflow,
 } from '@task-stream/api/tracker/domain';
 import { FindProjectsRepository } from '../ports/find-projects.repository';
@@ -49,6 +50,7 @@ export class IssueCreatedEventHandler
       assignee: users.ofNullable(issue.assigneeId),
       release: release ? { id: release.id, name: release.name } : null,
       parent: null,
+      rank: implicitRank(issue.number),
       labels: issue.labels,
       figmaUrl: issue.figmaUrl,
       storyPoints: issue.storyPoints,