Improve wrapper normalization and form presentation fidelity

[chubes4]

Summary

• Simplify wrapper-chain normalization while retaining source structure and editable descendants.
• Project authored header and footer selectors onto editor template-part wrappers, including non-terminal grid placement.
• Prevent imported links from navigating the editor canvas during block selection.
• Capture bounded form presentation metadata and resolve responsive custom-property references from controls and their ancestors.
• Preserve case-sensitive CSS custom-property names and explicitly sized or positioned button presentation.
• Restore editor presentation asset registration and align integration tests with the WordPress iframe asset lifecycle.

Verification

• PHP transformer validation and tests pass on PHP 8.2 through 8.5.
• WordPress site-plan integration passes on PHP 8.2 through 8.5.
• Generic visual-parity checks pass.
• Solved-site promotion passes: https://github.com/Automattic/blocks-engine/actions/runs/34162661482
• A paired Cindy Joy import produced nine pages with zero emitted fallback, HTML, freeform, or invalid blocks. Browser checks on that earlier candidate verified corrected textarea heights and safe editor link selection.

Remaining Site Work

The latest recorded Cindy Joy browser measurements still show textarea widths of 635px desktop and 300px mobile, compared with source widths of 611px and 280px. The companion source-class repair in Automattic/static-site-importer#1539 is active in that measurement but does not resolve the width difference. Full Cindy Joy visual parity is not claimed, and the earlier browser run is not a fresh full-site verification of the final asset-registration commit.

Related Work

Companion provider-wrapper class restoration: Automattic/static-site-importer#1539.

AI Assistance

GPT-6 Astra via OpenCode orchestrated implementation, review, browser investigation, CI repair, and verification across this branch. Earlier isolated implementation work also used GPT-5.6 Terra via OpenCode. The full commit scope and saved PR description were reviewed before merge.