Improve generic HTML layout and visual fidelity

[chubes4]

Summary

• preserve SVG webfont consumers and retain ambiguous entry shells through site-plan projection
• support grouped description lists and positioned inline geometry without invalid Gutenberg wrappers
• add an editable blocks-engine/author-layout companion block so authored flex/grid CSS remains the sole layout authority
• preserve direct control, RichText, semantic attribute, media, URL-resolution, and direct-child topology across generated blocks
• prefer neutral RichText output for phrasing-only layout containers instead of introducing a structural layout block

Architecture

Author-owned flex/grid islands no longer use core/group plus compensating block-gap CSS. Structural islands use a generated semantic companion block with InnerBlocks and no Gutenberg layout/block-gap support. Phrasing-only islands remain one editable RichText block. No generated !important rules are introduced.

Verification

• composer validate --strict
• composer test
• 258 PHP transformer parity fixtures
• package-install proof
• independent reviews of grouped lists, positioned carriers, selector identity, author-layout save contracts, topology, sanitization, and site-plan URL resolution

Closes #687
Closes #702
Closes #730
Closes #733
Closes #735

AI Assistance

OpenAI GPT-5.6 Sol via OpenCode drafted and iterated on substantive implementation and tests, performed codebase analysis, and ran verification. Chris Huber reviewed the architecture, prohibited compensating !important rules, and remains responsible for the submitted changes.