close-item should clearly report blocked archive closeout

[rickardvh]

During post-merge cleanup for PR #1210, I ran uv run agentic-planning close-item command-generation-schema-ownership --target . --reason ... --issue #1203 --format json.

The command returned exit 0, but it did not close the planning item. The JSON response only contained actions with kind: "manual review" and a warning:

• warning_class: archive_missing_closure_check
• message: Rename/refactor-like completed work is missing a stale-reference sweep in Validation Commands.

That warning is useful, but the command shape makes the no-op too easy to miss in automation or a long dogfooding session. I only caught it because agentic-workspace summary still showed queued items afterwards.

Suggested improvement:

• When close-item is blocked and does not remove the TODO item or archive the execplan, return a clear machine-readable status such as status: "blocked" / closed: false.
• Consider non-zero exit for command forms whose primary requested mutation did not happen, or provide an explicit --allow-warnings / --no-fail-on-blocked-closeout mode if exit 0 is intentional.
• Include the follow-up command or required field in a top-level next_action, not only in warning/action detail text.

Dogfooding context: stale active/queued command-generation execplans left after merge; cleanup required repeated close-item attempts and summary checks to verify state actually changed.