- RadioButtonGroup values for name/required override those of RadioButton

- Fix reactivity when RadioButton is used without group
- Use `readable` when writing is not required
- Use `readonly` to make intent clearer.
- Remove default values for `required` and `name`
  - More consistent with other input types
  - Means that `name` attribute will not be added for no reason

types/UIShell/Header.svelte.d.ts

@@ -30,6 +30,7 @@ export interface HeaderProps extends RestProps {
 
   /**
    * Specify the company name.
+   *
    * Alternatively, use the named slot "company" (e.g., `<span slot="company">...</span>`)
    * @default undefined
    */