Document repeatable HTML DOM box evidence capture

[chubes4]

Summary

• Documents the exact visual-parity dependency and browser install commands for DOM-box evidence capture.
• Adds the Homeboy artifact-origin dom-boxes command using dom-box-provider.mjs for generated .fig -> HTML artifact roots.
• Adds placeholder examples for Fisiostetic, FSE, and TT5 HTML artifact roots without committing local-only paths.
• Cross-links the workflow from the figma transformer parity docs.

Testing

• npm ci --prefix php-transformer/tools/visual-parity
• npm --prefix php-transformer/tools/visual-parity run install:browsers
• npm --prefix php-transformer/tools/visual-parity test

Notes

• Docs-only change; no helper script was added, so no new helper-specific tests were needed.
• Scope is limited to .fig -> HTML render evidence tooling/docs. No SSI or WordPress block conversion changes.

AI assistance

• AI assistance: Yes
• Tool(s): GPT-5.5 via OpenCode
• Used for: Drafted the documentation update, ran the existing visual-parity smoke test, and opened this PR under Chris's direction.