[SandObserver]

Summary

• Restructure docs/design-system.md into Color, Typography, Spacing and geometry, and Motion, with the spec ahead of the guidance in each section.
• Add the full palette table: light values and the -hi increased-contrast partners for all eighteen entries, with an inline swatch per value.
• Add the semantic layer values for both themes, and the surface tokens that resolve to palette greys.
• Document --sy-radius-md and the reduced-motion and reduced-transparency behaviour, none of which were covered.
• Replace the selector list of rules that sit off the type scale, which named eight rules under a count of six and matched neither the stylesheet nor the set the scale exempts.
• Move the Settings-page style assignments, the semantic value tables, the widget rules and the page-scoped tokens behind <details>.
• Remove file paths, test names, the theme storage key, and the rationale behind each decision.

Testing
All green, Docker build smoke test left to CI. No coverage change; the file carries no code.

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.
• CHANGELOG.md updated under Unreleased if the change is user-visible.