Preserve direct HTML description lists through a companion block

[chubes4]

Summary

• convert RichText-safe direct <dl>/<dt>/<dd> structures into a typed blocks-engine/description-list companion block
• preserve terms, descriptions, nested supported inline markup, classes, and exact inline CSS in editor and saved semantic markup
• retain the existing conservative fallback for malformed ordering, wrappers, block-level descriptions, and inline attributes Gutenberg RichText cannot round-trip
• aggregate one generated block definition and one Gutenberg-gap report across multi-page artifacts
• link diagnostics and implementation context to Gutenberg #4880 and stalled Gutenberg PR #20760

Closes #694.

Compatibility

This is an additive companion-block/result-report capability. Existing malformed or editor-unsafe description lists keep their prior fallback conversion. The companion contract is intentionally narrow so imported blocks can migrate to a native core Description List block if Gutenberg lands one.

Testing

• composer --working-dir=php-transformer test
• 29 Description List assertions
• 248 parity fixtures
• canonical contracts and all PHP transformer unit suites
• package-install proof
• generated index.js syntax check with Node
• git diff --check

Homeboy run agent-task-c386f13f-31e5-488e-b4fa-72b283e47e11 produced the isolated candidate. Its promotion gates lacked nested Composer hydration; that infrastructure gap is tracked in Extra-Chill/homeboy#10143. The same gate commands pass in the hydrated DMC worktree.

AI assistance

• Models: OpenAI GPT-5.6 Terra and OpenAI GPT-5.6 Sol
• Tools: Homeboy and OpenCode
• Used for: isolated implementation, dependency analysis, code review, editor-save correction, test execution, and upstream Gutenberg linkage with Chris Huber.