Add coverage baseline tooling

[roncodes]

Summary

• add Composer scripts to generate Pest coverage output and Clover XML
• add a repo-local coverage runner that fails early when PHP has no Xdebug/PCOV coverage driver
• add a repo-local Clover parser that prints line, method, and class coverage plus lowest-covered directories/files
• add CI coverage baseline generation using the existing Xdebug setup and upload the Clover report as an artifact
• ignore generated coverage and PHPUnit cache directories

Why

This PR establishes a measurable starting coverage percentage before adding more tests. Pest cannot produce coverage without a PHP coverage driver, so the runner now reports that prerequisite directly instead of running tests and failing later because coverage/clover.xml was never created.

Commands

• composer test:coverage
• composer test:coverage:clover
• composer coverage:summary
• composer coverage:baseline

Local and Docker requirement

Coverage requires one enabled PHP coverage driver:

• Xdebug with XDEBUG_MODE=coverage
• PCOV

If neither driver is loaded, composer coverage:baseline exits before running the suite and prints the PHP binary that needs the extension enabled.

Validation

• ./vendor/bin/pest --colors=never
• php -l scripts/coverage-runner.php
• php -l scripts/coverage-summary.php
• php scripts/coverage-summary.php /tmp/core-api-clover-sample.xml
• ./vendor/bin/php-cs-fixer fix -v --dry-run --config=.php-cs-fixer.php .github/workflows/ci.yml .gitignore composer.json scripts/coverage-runner.php scripts/coverage-summary.php
• /usr/local/bin/composer coverage:baseline now fails early with No PHP coverage driver is available on local PHP because neither xdebug nor pcov is loaded.