fix(kanban): promote dependents when a parent is archived

[Zyrixtrex]

What does this PR do?

Fixes a Kanban lifecycle inconsistency where archiving a parent task did not immediately unblock dependent children.

recompute_ready() already treats archived parents the same as done, but archive_task() was not triggering that promotion pass. As a result, children could remain stuck in todo until a later dispatcher tick.

This PR updates archive_task() to recompute ready tasks after a successful archive and adds a regression test covering the behavior.

Related Issue

No linked issue; found via code inspection.

Type of Change

• 🐛 Bug fix

Changes Made

• Added a regression test for archiving a parent with dependent children.
• Updated archive_task() to call recompute_ready(conn) after a successful archive.
• Kept the change scoped to a single Kanban lifecycle bug.

How to Test

1. Create a parent task.
2. Create a child task depending on that parent.
3. Confirm the child is in todo.
4. Archive the parent task.
5. Confirm the child is immediately promoted to ready.

Test Results

• pytest tests/hermes_cli/test_kanban_db.py -k "archive_task_triggers_recompute_ready_for_dependents or unlink_tasks_triggers_recompute_ready" -q
• Result: 2 passed

[teknium1]

Merged via PR #28372 (cherry-picked onto current main with your authorship preserved via rebase-merge — commit b7ea62e). Thanks for the contribution!