Add performance budget regression guardrails

[josiahking]

Summary

• add benchmark-only performance budget evaluation with pass/warn/fail/incomparable states
• add tracked regression calibration and reference artifacts for the accepted PHP 8.4.25 benchmark lane
• enforce evidence identity, cleanliness, source SHA, sample protocol, timing units, and normalized artifact integrity
• add a CI-safe benchmark policy job without running authoritative wall-clock timing on shared runners
• strengthen architecture/documentation guardrails for benchmark policy and CI workflow structure

Validation

• deterministic package split validation passed for all 7 packages
• release package validation passed
• skeleton create-project validation passed
• prerelease consumer validation passed
• benchmark policy passed: 22 tests, 139 assertions
• root quality passed: Deptrac, PHPStan, PHP-CS-Fixer, PHPUnit
• root PHPUnit: 679 tests, 2456 assertions, 1 skipped
• Composer audit: no security advisories
• license policy passed

Notes

• warm HTTP p50 budgets are EvolvePHP self-regression budgets, not competitor-relative rankings
• application_boot remains monitor-only
• shared GitHub-hosted runners validate policy/schema/smoke behavior only; authoritative absolute timing remains controlled evidence
• this change does not modify production framework runtime behavior