feat: add teardown script hook for worktree deletion

[BowgartField]

Summary

• Add scripts.teardown to jean.json — runs before a worktree is deleted
• If the teardown script fails, deletion is blocked and the worktree is restored
• Same environment variables as setup: JEAN_WORKSPACE_PATH, JEAN_ROOT_PATH, JEAN_BRANCH

Example

{
  "scripts": {
    "setup": "npm install",
    "teardown": "docker compose down",
    "run": "npm run dev"
  }
}

Test plan

• Add a teardown script to jean.json and verify it runs on worktree deletion
• Test with a failing script (exit 1) — deletion should be blocked, worktree reverts to 'ready'
• Test without a teardown script — deletion works as before
• Verify permanently_delete_worktree (archived) is unaffected