python-dev SKILL.md: add Pydantic/Protocol wisdom from lkml sprint

[rjgladish]

Summary

The python-dev skill at ~/.claude/skills/python-dev/SKILL.md needs updating:

1. Fix mypy → ty — SKILL.md line 14 still says mypy --strict, should be ty
2. Add Pydantic construction patterns — create_model() for dynamic model building
3. Add Protocol/issubclass trap — non-method members cause silent discovery failure
4. Add plugin discovery patterns — pkgutil + importlib auto-discovery
5. Reference python-dev pack learnings — Packs/python-dev/learnings/

Learnings Source

Pack: substrate/Packs/python-dev/ (commit 2d3af61)

• pydantic-create-model-patterns.md
• protocol-issubclass-trap.md
• plugin-discovery-patterns.md

Work Items

• Fix mypy references → ty in SKILL.md
• Add "Wisdom" section referencing pack learnings
• Add use-when triggers for new patterns
• Compose full wisdom document from accumulated learnings (follow-up)

Context

Source: lkml sprint WA2 (pydantic rewrite) and WA4 (plugin discovery)