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/domain/src/index.ts

@@ -6,6 +6,7 @@ export * from './lib/issue/issue-attachment';
 export * from './lib/issue/mentions';
 export * from './lib/issue/issue-hierarchy';
 export * from './lib/issue/issue-checklist';
+export * from './lib/issue/issue-rank';
 export * from './lib/project/project-settings';
 export * from './lib/comment/comment';
 export * from './lib/release/release';