fix: detect Python package manager before installing in worktree setup

[kuishou68]

Closes #1108

Problem

The using-git-worktrees skill unconditionally ran poetry install for any project containing a pyproject.toml:

# Old code
if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
if [ -f pyproject.toml ]; then poetry install; fi

pyproject.toml is now the standard Python project metadata file — it is used by uv, pip, hatch, pdm, setuptools, and many other tools, the vast majority of which are not Poetry. Running poetry install on these projects either fails outright (if Poetry is not installed) or produces an incorrect environment.

Fix

Detect the actual package manager by inspecting file contents and lock files:

# New code
if [ -f pyproject.toml ]; then
  if grep -q '\[tool\.poetry\]' pyproject.toml; then
    poetry install
  elif [ -f uv.lock ]; then
    uv sync
  elif [ -f requirements.txt ]; then
    pip install -r requirements.txt
  else
    pip install -e .
  fi
elif [ -f requirements.txt ]; then
  pip install -r requirements.txt
fi

Detection heuristic:

Signal	Action
[tool.poetry] in pyproject.toml	poetry install
uv.lock present	uv sync
requirements.txt present	pip install -r requirements.txt
Generic pyproject.toml	pip install -e .
Only requirements.txt	pip install -r requirements.txt

Poetry projects are still handled correctly. Non-Poetry projects now get an appropriate install command instead of a Poetry error.

Changed Files

• skills/using-git-worktrees/SKILL.md: updated "Run Project Setup" section

[Bortlesboat]

I verified the issue against current main locally, and this keeps the fix nicely scoped to the broken Run Project Setup snippet in skills/using-git-worktrees/SKILL.md.

One follow-up worth considering, but not necessarily a blocker for this PR: uv-managed projects can exist without a committed uv.lock, so [tool.uv] (or a similarly explicit signal in pyproject.toml) may eventually be worth checking too. Even with that edge case, this is still a clear improvement over unconditional poetry install for every pyproject.toml project.