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/presenters/src/lib/graphql/enums.ts

@@ -1,4 +1,5 @@
 import { registerEnumType } from '@nestjs/graphql';
+import { IssueSort } from '@task-stream/api/tracker/application';
 import {
   IssueLinkType,
   IssuePriority,
@@ -23,6 +24,10 @@ registerEnumType(IssueLinkType, { name: 'IssueLinkType' });
 registerEnumType(ProjectRole, { name: 'ProjectRole' });
 registerEnumType(ReleaseStatus, { name: 'ReleaseStatus' });
 registerEnumType(LinkDirection, { name: 'LinkDirection' });
+registerEnumType(IssueSort, {
+  name: 'IssueSort',
+  description: 'RECENT: last updated first. RANK: backlog order.',
+});
 registerEnumType(NotificationKind, {
   name: 'NotificationKind',
   description: 'Why someone is told',