Capture malformed PHPUnit bootstrap payloads

[chubes4]

Summary

• execute generated PHPUnit PHP inside an outer diagnostic boundary
• persist ParseError and other pre-handler throwables before rethrowing
• retain the existing inner recorder for fatal and non-fatal bootstrap exits
• prove malformed generated PHP in a real Playground runtime

Root cause

After #1932 captured exit()/die(), current Intelligence CI still produced no marker. That means the generated payload fails before its first shutdown callback can register. Directly submitted malformed PHP has the same behavior; wrapping evaluation lets WP Codebox persist the parse failure first.

Verification

• npm run build
• npm run test:phpunit-runtime-failure-diagnostics
• npm run test:playground-phpunit-bootstrap-failure-integration
• git diff --check

Fixes #1916