Redesign PhoneInput #61

Bring PhoneInput to shadcn-registry quality. Depends on #58.

• Single input group with the focus ring on the whole field (currently clipped on the inner input); aria-invalid styling.
• Country menu matching LanguageSwitcher: animation, flip, search with clear, empty state.
• New props: size, countries (restrict / reorder), align, side, searchPlaceholder, emptyMessage, classNames.
• Backward compatible.