Add DOM-box quality metrics for Figma HTML artifacts

[chubes4]

Summary

• Add a fixture-matrix DOM-box analyzer that converts captured rendered HTML boxes into actionable quality metrics and per-page findings.
• Emit dom-box-quality.json beside captured dom-boxes.json during .fig -> HTML matrix runs and roll DOM metrics into fixture/matrix readiness totals.
• Extend the DOM-box provider to include a bounded list of visible rendered elements missing the configured node-id attribute so missing data-figma-node-id boxes can be diagnosed.

Metrics added

• dom_horizontal_overflow_count
• dom_viewport_width_leak_count
• dom_huge_vertical_spacing_count
• dom_collapsed_box_count
• dom_offscreen_box_count
• dom_missing_node_id_box_count
• per-page risk_score and risk_bucket, plus matrix rendered_dom_boxes risk category totals

Evidence

• Verified existing Fisiostetic DOM-box capture with the new analyzer.
• Sample local operator report: /var/folders/lr/c_cmmt7s0592m4njz99v5yb40000gn/T/opencode/figma-html-render-evidence-20260706/fisiostetic-dom-box-quality.json
• Fisiostetic summary from that capture: 220 DOM boxes, 11 collapsed boxes, risk bucket high, no horizontal overflow or viewport-width leaks.

Tests

• composer test in figma-transformer
• npm ci in php-transformer/tools/visual-parity
• npm test in php-transformer/tools/visual-parity
• git diff --check

Limitations

• The analyzer is threshold-based rendered DOM diagnostics; it does not compare against source screenshots or Figma geometry.
• Existing historical dom-boxes.json files only expose missing node-id boxes if the provider/report included unidentified elements. New captures include a bounded unidentified_elements list.
• Sample evidence path is local operator evidence, not reviewer-hosted artifact storage.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode with openai/gpt-5.5
• Used for: Implemented the DOM-box analyzer, fixture-matrix wiring, provider diagnostics, tests, verification, and PR drafting under Chris's direction.