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.
TDD implementation of three navigation widgets: mobile overlay toggle,
fixed sidebar with IntersectionObserver-driven active section tracking,
and utility bar with contact info and CV download action.
Ilia Mashkov