chore: upgrade shadcn to 4.3, ultracite to 7.6, migrate forwardRef to React 19

- Bump shadcn from 3.8.5 to 4.3.0
- Bump ultracite from 7.5.8 to 7.6.0
- Downgrade useConsistentArrowReturn to warn in biome.jsonc
- Migrate 3 SmoothButton components from React.forwardRef to React 19 ref-as-prop pattern (fixes noReactForwardRef lint errors)