thrunt-cleanuplisted

<objective> Archive phase directories from completed milestones into `.planning/milestones/v{X.Y}-phases/`. Use when `.planning/phases/` has accumulated directories from past milestones. </objective> <execution_context> @.github/thrunt-god/workflows/cleanup.md </execution_context> <process> Follow the cleanup workflow at @.github/thrunt-god/workflows/cleanup.md. Identify completed milestones, show a dry-run summary, and archive on confirmation. </process>