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/infrastructure/src/lib/mongo/find.repositories.ts

@@ -9,6 +9,7 @@ import {
   FindReleasesRepository,
   FindTimelineRepository,
   IssueFilter,
+  IssueSort,
   Page,
 } from '@task-stream/api/tracker/application';
 import {
@@ -135,7 +136,11 @@ export class MongoFindIssuesRepository extends FindIssuesRepository {
     const [docs, total] = await Promise.all([
       this.issues
         .find(query)
-        .sort({ updatedAt: -1 })
+        .sort(
+          filter.sort === IssueSort.RANK
+            ? { rank: 1, number: 1 }
+            : { updatedAt: -1 },
+        )
         .skip(filter.offset)
         .limit(filter.limit)
         .lean<IssueDoc[]>(),