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/commands/commands.spec.ts

@@ -33,6 +33,7 @@ import {
 import { TrackerStreamsRepository } from '../ports/tracker-streams.repository';
 import { IssueTree } from './issue-tree';
 import { SetIssueParentCommand } from './set-issue-parent.command';
+import { RankIssueCommand } from './rank-issue.command';
 import {
   AddChecklistItemCommand,
   UpdateChecklistItemCommand,
@@ -372,6 +373,38 @@ describe('tracker commands (event sourced)', () => {
     });
   });
 
+  it('orders the backlog from the ranks in the event store', async () => {
+    const { run, rehydrator } = await setup();
+    const projectId = await projectWithTeam(run);
+    const ids = [];
+    for (const title of ['A', 'B', 'C'])
+      ids.push(
+        (
+          await run(
+            new CreateIssueCommand('dev', projectId, IssueType.TASK, title, {}),
+          )
+        ).id,
+      );
+    const [a, b, c] = ids;
+
+    // C to the top, then B between C and A: C, B, A.
+    await run(new RankIssueCommand('dev', c, null, a));
+    await run(new RankIssueCommand('dev', b, c, a));
+    const ranks = await Promise.all(
+      [c, b, a].map(
+        async (id) => (await rehydrator.rehydrate(id, Issue)).backlogRank,
+      ),
+    );
+    expect([...ranks].sort()).toEqual(ranks);
+    // Neighbours given the wrong way round: the order changed meanwhile.
+    await expect(run(new RankIssueCommand('dev', a, b, c))).rejects.toThrow(
+      BusinessRuleError,
+    );
+    await expect(run(new RankIssueCommand('pm', a, null, c))).rejects.toThrow(
+      ForbiddenError,
+    );
+  });
+
   it('does not let viewers modify tickets', async () => {
     const { run } = await setup();
     const projectId = await projectWithTeam(run);