docs: align README, Fern docs, and skills for agent/python/rest workflows

[willkill07]

Summary

• Align documentation for three primary audiences: coding agents, Python API users, and REST API users.
• Improve onboarding and consistency across README, CONTRIBUTING, AGENT, Fern docs, and skill playbooks.
• Add a new Fern REST integration quickstart and clarify generated-doc artifact workflow (openapi.json, config schema, Python reference).
• Harden the Python reference generation pipeline to remove empty Usage headings.
• Update skill docs to include clearer validation/cross-links and explicit pre-commit hook behavior (re-stage and re-run commit when hooks auto-fix files).
• Remove duplicate * 2.* shadow files that could cause doc drift/confusion.

Key Changes

• README.md: audience routing, naming cheat sheet, end-to-end REST lifecycle examples.
• CONTRIBUTING.md: corrected API usage examples and release/docs guidance.
• Fern docs:
  • Added fern/docs/pages/rest/quickstart.mdx
  • Updated nav in fern/docs.yml
  • Updated welcome/python/config pages for discoverability and regeneration guidance.
• Generated artifacts:
  • Added/tracked fern/openapi.json
  • Added/tracked fern/docs/assets/combined-config.schema.json
  • Refreshed fern/docs/pages/python/reference.mdx
• scripts/gen_python_api_mdx.py: strip empty generated Usage sections.
• Skills:
  • Standardized guidance in CI/docs/CLI/API/writers/PR skills
  • Added explicit “hooks may modify files; re-stage and re-commit” instructions.