✨ Add cleanup-worktree command for post-merge cleanup

Adds a command to safely remove git worktree directories after their PRs
have been merged. Verifies merge status before cleanup, preserves all
branches, and returns user to the primary repo on main.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Nick Sullivan

plugins/core/commands/cleanup-worktree.md

@@ -0,0 +1,35 @@
+---
+description: Clean up a git worktree after its PR has been merged
+model: haiku
+---
+
+# Cleanup Git Worktree
+
+<objective>
+Safely remove a git worktree directory after its associated PR has been merged to main,
+preserving branches and leaving the user in the primary repo ready for the next task.
+</objective>
+
+<merge-verification>
+Confirm the worktree's branch was merged before any cleanup. Pull main in the primary
+repo to get the latest state, then verify the branch appears in the merged history.
+
+If the branch is unmerged, stop and explain the situation. Merged work is safe to clean
+up; unmerged work requires user decision.
+</merge-verification>
+
+<cleanup-scope>
+Remove only the worktree directory itself. Preserve all branches (local and remote) for
+git history and potential future reference.
+
+Use `git worktree list` to find the primary repo location. The current working directory
+may be inside the worktree being cleaned up, so navigate to the primary repo first.
+</cleanup-scope>
+
+<success-criteria>
+Worktree directory removed, all branches preserved, user returned to primary repo on
+main with latest changes pulled.
+
+Celebrate the successful merge with congratulatory language acknowledging the completed
+work.
+</success-criteria>