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/issues.service.ts

@@ -15,6 +15,7 @@ import {
 import { DetachFileCommand } from './commands/detach-file.command';
 import { WatchIssueCommand } from './commands/watch-issue.command';
 import { SetIssueParentCommand } from './commands/set-issue-parent.command';
+import { RankIssueCommand } from './commands/rank-issue.command';
 import {
   AddChecklistItemCommand,
   RemoveChecklistItemCommand,
@@ -218,6 +219,18 @@ export class IssuesService {
     );
   }
 
+  /** Moves a ticket in the backlog between `above` and `below` (null: an end). */
+  rank(
+    actorId: string,
+    issueId: string,
+    above: string | null,
+    below: string | null,
+  ): Promise<CommandResult> {
+    return this.commandBus.execute(
+      new RankIssueCommand(actorId, issueId, above, below),
+    );
+  }
+
   addChecklistItem(
     actorId: string,
     issueId: string,