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/ports/find-issues.repository.ts

@@ -7,6 +7,11 @@ import {
   StatusCategory,
 } from '@task-stream/api/tracker/domain';
 
+export enum IssueSort {
+  RECENT = 'RECENT',
+  RANK = 'RANK',
+}
+
 export interface IssueFilter {
   projectId: string;
   /** Status, type and area ids of the project's settings. */
@@ -21,6 +26,8 @@ export interface IssueFilter {
   labels?: string[];
   /** Only the tickets hanging from this one. */
   parentId?: string;
+  /** RECENT (default): last updated first. RANK: backlog order. */
+  sort?: IssueSort;
   search?: string;
   limit: number;
   offset: number;