JohnXu22786/worktree-mgr: Automatically create isolated git worktrees for DSH tasks

`worktree-mgr` is an MIT-licensed plugin for DSH designed to address issues of change pollution and merge chaos caused by parallel tasks sharing repository workspaces. By automatically creating isolated git worktrees, it enables the full lifecycle management of task workspaces, including creation, synchronization, merging, and cleanup. The plugin supports Node.js 21+ and provides five model tools and a CLI. Its core capabilities include task-driven automatic branch and path generation, branch name security validation, uncommitted changes detection, merge target consistency verification, and concurrency-safe mutex locks. Its design emphasizes the separation of synchronization and cleanup, supports batch processing with fail-safe operation, and includes automatic rollback upon creation failure as well as cross-platform trigger support. Users can install or enable the plugin locally via the `dsh` command and use the `wtm` CLI to perform operations such as starting, viewing status, merging, and cleanup.