Upgrade final-form to v5 for react-final-form compatibility

react-final-form v7 requires final-form ^5.0.0 as a peer dependency.
Also fixed UseFieldConfig type which is no longer generic in v5.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: alaister

website/components/forms/FormInput.tsx

@@ -15,7 +15,7 @@ export interface FormInputProps extends PropsWithoutRef<
   type?: 'text' | 'password' | 'email' | 'number'
   outerProps?: PropsWithoutRef<JSX.IntrinsicElements['div']>
   labelProps?: ComponentPropsWithoutRef<'label'>
-  fieldProps?: UseFieldConfig<string>
+  fieldProps?: UseFieldConfig
 }
 
 const FormInput = forwardRef<HTMLInputElement, FormInputProps>(