Modernize python-dev skill to use uv exclusively

[robkisk]

Summary

• Rewrote Environment Management section in the python-dev skill to use uv exclusively — removed all references to pip, python3 -m venv, conda, requirements.txt, and manual venv activation
• Added dedicated Code Quality subsections for Ruff (linting & formatting) and Pyright (type checking) with runnable command examples
• Updated Best Practices summary to reflect the modern toolchain (uv, Ruff, Pyright)

Motivation

The skill previously contained conflicting guidance — it mentioned uv alongside venv, pip install, and requirements.txt, leaving ambiguity about which workflow to follow. This aligns the skill with the Astral.sh toolchain (uv + ruff) that the project already uses.

What changed

Section	Before	After
Dependency Management	uv or venv, check .venv, activate	uv exclusively, pyproject.toml only
Environment Setup	Shell script with venv/pip/uv pip	uv sync / uv run / uv add examples
Script Execution	"Activate venv, use python3"	uv run — no activation needed
Code Style	Single Ruff bullet	Full Ruff section (check, fix, format)
Type Checking	Not mentioned	Pyright section
Best Practices #6	"uv or venv, activate before use"	uv exclusively, Ruff, Pyright

What was removed

• pip install -r requirements.txt
• python3 -m venv .venv / source .venv/bin/activate
• uv pip install (deprecated subcommand pattern)
• requirements.txt as a dependency source

Test plan

• Verify no remaining references to pip, venv (as a tool), or requirements.txt in the skill file
• Confirm markdown renders correctly (no broken code fences)
• Validate skill passes .github/scripts/validate_skills.py in CI