backend
Create the foundational structure for managing design-system CSS with
co-located sources and semantic tokens:
- Add `cmd/buildstyles` to concatenate ordered CSS sources into a single
shipped stylesheet
- Define semantic color and effect tokens in `internal/web/ui/base.css`
- Move primitive and catalog CSS sources from `static/css/` to
co-located locations under `internal/web/ui/`
- Update test contract to verify token presence and proper stylesheet
generation
- Regenerate `static/styles.css` with new semantic token layer and
source annotations
