Initial commit: FA Design System source files

Copy of the Funeral Arranger design system components, theme, tokens,
and Storybook config from the original Parsons project. Pre-upgrade
baseline with React 18, MUI v5, Storybook 8.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/molecules/CartButton/index.ts

@@ -0,0 +1,2 @@
+export { default } from './CartButton';
+export * from './CartButton';