Add modernization scaffolding for Art→IPF migration and PHP 8.2–8.5 support

[fiammybe]

Set up CI, static analysis, coding standards, and migration documentation so the Art → IPF refactor can happen incrementally and safely.

Checklist:

• Add GitHub Actions for PHP lint and matrix builds (PHP 8.2, 8.3, 8.4, 8.5)
• Add coding standards and static analysis (e.g. PHPStan, code style tools)
• Add docs:
  • migration/refactor matrix (Art classes and their migration targets)
  • PHP 8 compatibility known issues
  • phased refactor/PR plan
• Add centralized module bootstrap/helper for handler loading and config access
• Confirm no feature changes