feat: add /worktree skill — git worktree lifecycle management

[agi-bootstrap]

Summary

• Adds a new /worktree skill for git worktree lifecycle management
• Four subcommands: start, merge, clean, list
• Wraps Claude Code's built-in EnterWorktree/ExitWorktree with a structured workflow: base branch confirmation, dependency bootstrap (npm/yarn/pnpm/bun/pip/poetry/bundler), state tracking via ~/.gstack/worktree-active.json, and safe merge/clean with unmerged-work guards

Why

Worktrees are central to the parallel sprint workflow described in the README — Conductor creates isolated workspaces, /ship and /review run in them. But there's no skill for the manual worktree lifecycle: starting a feature branch in isolation, merging it back, or discarding it safely. This fills that gap.

What it does

Subcommand	Behavior
/worktree start <name> [--from <branch>]	Creates worktree, confirms base branch, bootstraps deps, switches session into it
/worktree merge	Checks for uncommitted changes, exits worktree, merges branch, cleans up
/worktree clean [--force]	Refuses if unmerged commits exist (unless --force), confirms with user, removes worktree + branch
/worktree list	Shows all worktrees + active state

Safety: merge gates on uncommitted changes, clean refuses to discard unmerged work without --force, and even with --force it confirms before deleting.

Test plan

• /worktree start test-feature — creates worktree, switches session, bootstraps deps
• /worktree list — shows the new worktree and active state
• Make a commit in the worktree, then /worktree merge — merges back to base branch
• /worktree start throwaway, then /worktree clean — refuses (has unmerged commit)
• /worktree clean --force — confirms and removes

🤖 Generated with Claude Code