feat: add ChatGPT Skill adapter

[WilliamWang1721]

What changed

• add .chatgpt/ponytail/, a standard single-Skill ChatGPT adapter with one root SKILL.md and agents/openai.yaml
• route Ponytail's core, review, audit, debt, gain, and help behavior through that entrypoint
• generate the six reference files from the canonical skills/ bodies so the adapter cannot drift
• add parity tests that check generated content, validate the frontmatter shape, and ensure the bundle contains exactly one SKILL.md

Why

The repository's canonical distribution contains six independent SKILL.md entrypoints. That works for skill-capable agent hosts, but a ChatGPT upload intended to behave like one Ponytail plugin needs one entrypoint.

The adapter keeps the canonical skill bodies as generated references and handles mode changes in conversation instead of trying to run Claude Code, Codex, or Copilot lifecycle hooks that ChatGPT does not support.

Usage

Regenerate the adapter after changing a canonical skill:

node scripts/build-chatgpt-skill.js
node --test tests/chatgpt-skill.test.js

Create an uploadable archive:

cd .chatgpt
python3 -m zipfile -c skill.zip ponytail

Validation

• node --test tests/chatgpt-skill.test.js — 10 passing
• OpenAI Skill validator — valid
• ZIP integrity and single-entrypoint checks — passing

Built against upstream main at 16f29800fd2681bdf24f3eb4ccffe38be3baec6b.