fix(kanban): demote ready children when a parent is reopened

[Drexuxux]

Summary

Fix a Kanban dashboard state invalidation bug where reopening a completed parent task could leave dependent children incorrectly visible in ready.

When an operator moves a parent task from done or archived back into active work, any directly dependent child that was previously unblocked by that parent should stop advertising itself as ready immediately. Before this change, the dashboard could keep showing a stale ready child until a later claim-time guard corrected it.

What Changed

• update the dashboard status transition helper to detect when a task leaves a satisfied dependency state (done / archived)
• immediately demote directly linked ready children back to todo
• emit a child status event with reason: "parent_reopened" so the transition is observable

Why This Matters

The dispatcher already protects the invariant at claim time, but the dashboard UI was still capable of showing stale-ready work after a parent was reopened. This patch brings the visible board state back in line with the actual dependency model immediately, instead of waiting for a later recovery point.

Tests

Passed targeted regression coverage:

• test_patch_drag_drop_move_todo_to_ready
• test_reopening_parent_demotes_ready_child
• test_patch_status_running_rejected

[teknium1]

Merged via PR #28382 (cherry-picked onto current main with your authorship preserved via rebase-merge — commit 917e518). Thanks for the contribution!