## Summary
Implement the `git_worktree_list` tool that parses `git worktree list` output into structured data with path, branch, commit hash, and current directory marker.
## Changes
- Implemented `parseWorktreeList()` helper to parse raw `git worktree list` output
- Handles standard branches (e.g., `[main]`)
- Handles detached HEAD (marked as `(detached)`)
- Marks the current working directory with `isCurrent: true`
- Wired parser into `git_worktree_list` tool execute function
- Returns both formatted display text and structured `details.worktrees` array
- Added error handling for non-git-repo directories
- Restructured tool definitions inside extension factory to capture `pi` via closure
## Testing
- [x] Parsing logic verified against real `git worktree list` output (3 worktrees)
- [ ] Manual verification in pi TUI pending extension load test
## Checklist
- [x] Self-reviewed the diff
- [x] Code follows project conventions (AGENTS.md, DESIGN.md, DOMAIN.md)
- [x] Descriptive naming (no single-character variables)
- [x] Error handling with clear messages and suggestions
Co-authored-by: David Kong <davkon@gmail.com>
Reviewed-on: #16
