Wires tailwind.config.ts to every custom-property token in styles.css
(spacing, OKLCH colours, radii, z-index, sizing, durations) so Tailwind
utilities resolve to the same variables the vanilla CSS uses. Adds
ThemeContext/useTheme as a React port of theme.ts, keeping the same
localStorage keys and data-theme/data-palette attributes so it can run
alongside the vanilla shell.
