design: two-color palette — rename all tokens to --cream / --blue

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.

src/widgets/Navigation/ui/UtilityBar.test.tsx

@@ -23,7 +23,7 @@ describe('UtilityBar', () => {
     it('Download CV button has primary variant class', () => {
       render(<UtilityBar />);
       const btn = screen.getByRole('button', { name: /download cv/i });
-      expect(btn).toHaveClass('bg-burnt-oxide');
+      expect(btn).toHaveClass('bg-blue');
     });
   });
 });