chore: install ardenthq/ai conventions

[alfonsobries]

Adds the shared @ardenthq/airc conventions to php-crypto.

This repo had no committed CLAUDE.md, so it's a clean from-scratch run: npx @ardenthq/airc install creates CLAUDE.md with the @import lines, drops the guidelines into .claude/ardenthq/, and ignores CLAUDE.local.md. It's a plain PHP SDK (no Laravel, no Node project), so it picks up core + php and runs through the standalone CLI — no composer or npm dependency.

composer.json gets a post-update-cmd hook so the managed files re-sync on every composer update.

Output:

✓ ardenthq-ai
  wrote core.md, php.md
  created CLAUDE.md with imports
  added CLAUDE.local.md to .gitignore

Recommended (not yet installed):
  laravel/pint — Standalone code formatter (works without Laravel). Backs `composer format`.
    composer require --dev laravel/pint

Skip recommendations: export ARDENTHQ_AI_QUIET=1

https://app.clickup.com/t/2570579/86e1nmjd9

⚠️ Depends on releasing @ardenthq/airc to npm — until then npx @ardenthq/ai won't resolve.