Replace ochre-clay, carbon-black, burnt-oxide, slate-indigo with clean
two-color system: --cream (#f4f0e8) and --blue (#041cf3). Update every
component, utility class, and test assertion.
Installs @storybook/nextjs-vite. Stories co-located with components,
grouped by layer (Shared/Entities/Widgets). Multi-variant cases use
render functions instead of one story per variant/size.
Ilia Mashkov