Fix #1060: gate wrapper coalescing on geometry proof

[chubes4]

Summary

• validate optional, hash-bound layout geometry proof by stable structural source-node selectors
• apply accepted reductions at the common conversion boundary while preserving explicit runtime, interaction, role, ID, and motion-owned wrappers
• permit exact reductions without corrective CSS and validate target geometry rather than requiring the removed wrapper box to survive
• prune source-empty wrappers without visual/runtime/semantic evidence and avoid assigning price identity to generic ancestors from descendant text

Verification

• composer test
• canonical contracts passed
• 280 parity fixtures passed
• package-install proof passed

Greek Corner acceptance

The preserved public-site capture was compiled with six hash-bound Catering reductions measured at 390px and 1440px. Removing all six wrappers produced zero full-document geometry delta and zero selected computed-style changes at both viewports.

• source: https://www.greekcorner.us/
• source path: website/catering-1/index.html
• source SHA-256: ddc9c54c41cf7c55c4c9aa1d3e35fb1cae5e2f2e05c7129a278ef80ca9f453bc
• reductions accepted/applied: 6/6
• compile status: success_with_warnings
• fallback blocks: 0
• editability-policy failures: 0
• remaining diagnostics: 21 author_layout_topology_changed warnings

Without the proof payload, the same capture remains conservative: Catering reports depth 26 against the maximum 20. With the measured proof, Catering and Menu both satisfy the required editability policy without relaxing thresholds.

Closes #1060.

AI assistance: OpenAI gpt-5.6-sol via OpenCode compared the competing implementations, refined the generic proof contract, generated browser measurements for the preserved corpus, implemented the fixes and tests, and ran all verification. Chris Huber remains responsible for the change.