Add PHP quality workflow, migration docs, and shared bootstrap helper

[Copilot]

This PR adds repository-level PHP quality checks for supported runtimes and documents the Art → IPF migration path without changing module behavior. It also introduces a shared bootstrap/helper entry point for module access and handler loading, kept out of existing runtime wiring in this slice.

• CI: PHP quality workflow

  • Adds a new GitHub Actions workflow covering PHP 8.2, 8.3, 8.4, and 8.5
  • Runs:
    • PHP lint across src/
    • coding standards via PHPCS
    • static analysis via PHPStan
  • Adds minimal repo config for PHPCS and PHPStan to support the new checks

• Developer documentation

  • Adds an Art → IPF migration matrix to map legacy areas to intended IPF-oriented targets
  • Adds a PHP 8 compatibility checklist for reviewing legacy code under the supported runtime matrix
  • Adds a phased refactor roadmap to sequence follow-up work without mixing it into this PR
  • Links the new docs from docs/index.md

• Shared bootstrap/helper

  • Adds src/include/bootstrap.php as a single place for:
    • module dirname lookup
    • module path resolution
    • shared module access
    • shared handler loading
  • Keeps the helper additive for now so existing entry points and handlers continue to behave as-is

• Compatibility cleanup

  • Corrects a pre-existing syntax error in src/class/art/functions.locale.php so the new lint gate can evaluate the full module tree

function &iforum_get_handler($handlerName)
{
    $handler = icms_getmodulehandler($handlerName, iforum_get_module_dirname(), 'iforum');

    return $handler;
}