Preserve textual anchors during button recognition

[chubes4]

Summary

• require explicit role or resolved visual surface evidence before promoting anchors to core/button
• preserve underlined textual CTAs, navigation/legal links, and unstyled action links as anchors
• retain true stylesheet-backed CTA rows and native buttons as editor-valid button blocks
• project authored button selectors onto the rendered inner link
• preserve accessible labels in canonical button attributes

Verification

• composer test
• canonical contracts
• 28 button classifier assertions
• 249 parity fixtures
• package install proof
• PHP lint and git diff --check

Fixture 37 hero CTA and footer legal links remain plain anchors; explicit styled stream-btn and native button fixtures remain buttons.

Compatibility

Detection is intentionally conservative: unstyled anchors remain links unless they declare role=button or a resolved fill/border/radius surface. No commerce- or fixture-specific exceptions were added.

Merge order

Blocks Engine #711 may merge first; retain both branches test additions when resolving the two expected test-file conflicts.

AI assistance

OpenAI GPT-5.6 Sol via OpenCode implemented and iteratively repaired the semantic classifier through canonical/parity review. Chris Huber reviewed and remains responsible for every line.

Fixes #709.