docs: stabilize edge fragment geometry

[sylvain-wei]

Summary

• keep the interactive paper-text fragments visually tilted without rotating their hit boxes
• prevent transformed edge fragments from expanding the page canvas
• replace the oversized rotated browser focus ring with a restrained inset focus treatment
• deterministically finalize recomposition sooner in throttled browsers
• rebuild the release manifest

Validation

• html-validate docs/index.html
• csstree-validator docs/styles.css
• node --check docs/script.js
• shell syntax validation
• git diff --check
• python scripts/rebuild_manifest.py
• python verify_release.py

The local Playwright package was available, but this runner could not obtain its Chromium binary because the download endpoint returned an empty/truncated archive; browser claims are therefore limited to the previously verified interaction plus post-merge Pages checks.