Adds the CCA-Audit skill following the CONTRIBUTING.md guidelines:

• cca-audit/SKILL.md — full skill definition with YAML frontmatter and all required sections (When to Use, What It Does, How to Use, Example, Tips, Common Use Cases)
• README entry added alphabetically under "Development & Code Tools"

What it is: A 6-layer parallel code audit pipeline with non-overlapping scopes. Runs 6 specialized auditors (code quality, bugs, security, performance, docs, config) in parallel, deduplicates findings, auto-fixes P1+P2, re-verifies with tests, and gates through an architect review.

Full source and additional variants (Codex CLI, OpenRouter Python CLI) at github.com/GiulioDER/cca-audit. MIT licensed.