Load generated presentation styles in the block editor

[chubes4]

Summary

• load global and route-scoped generated CSS inside Gutenberg iframe settings
• preserve deterministic presentation identities for runtime coverage checks
• keep native video markup editor-valid and preserve responsive image semantics through a sanitized, explicit fallback
• add contract, parity, and WordPress integration coverage

Dependency

• Editor evidence consumer: Capture editor iframe presentation coverage wp-codebox#2253

Verification

• composer test
• 275 PHP transformer parity fixtures
• composer test:wordpress-integration is defined but requires WP_TESTS_DIR, which is unavailable locally

AI assistance

OpenAI gpt-5.6-sol was used through OpenCode to inspect WordPress block-editor behavior, implement the stylesheet and responsive-media contracts, and add regression coverage. Chris Huber reviewed and is responsible for the changes.