Redesign TranslationWidget #63

Bring TranslationWidget to shadcn-registry quality. Depends on #58 and the LanguageSwitcher redesign (#59).

• Replace the neumorphic styling with a tokenised two-pane card.
• Header with ghost language pickers and an animated swap button.
• Toolbar: character count (maxLength), clear, copy-to-clipboard with live-region feedback.
• loading state with skeleton and aria-busy.
• New props: showCount, showCopy, showClear, maxLength, loading, onTargetCopy, defaultSourceText, classNames.
• Backward compatible.