Add skill: codex-pet-generator

[wyddy7]

Adds codex-pet-generator to skills/.curated/.

A skill for generating readable Codex desktop pets. Encodes the workflow that turns single-shot full-sheet generation
into a row-by-row approach with explicit approved/unapproved gating, deterministic packing of per-frame inputs into
the required 1536×1872 / 8×9 grid, and a validator that checks the spritesheet plus the pet.json install contract.

Source repo: https://github.com/wyddy7/codex-pet-generator (MIT, v0.1.0)

Why curated:

• Solves a specific Codex-shaped problem (the 72-frame sheet failure mode at desktop sprite size)
• Self-contained — manual slicing is documented but no external dependencies beyond Pillow
• Includes a validator that enforces the install contract Codex actually checks at load time

Bundle:

• SKILL.md — workflow, prompting rules, slicing/packing rules
• references/ — row semantics, acceptance ladder, slicing guide
• scripts/ — packer + validator (Python, Pillow only)
• agents/openai.yaml — Codex UI metadata
• LICENSE.txt — MIT