feat: UI color theming system with live preview, presets and server sync

- RGBA color picker with live preview (debounce 50ms)
- 30 preset colors + 12 theme presets (Ocean, Forest, Sunset, Royal, etc.)
- Header image selection from configurable image library
- Export/Import theme as JSON via clipboard
- CSS variable theming across all UI elements: NitroCard headers/tabs,
  context menus, buttons (primary/dark/gray), InfoStand, toolbar,
  room tools, purse, progress bars, sliders
- All elements use var(--name, fallback) for zero visual change when default
- Smooth 0.3s CSS transitions on theme change
- Server-side persistence via WebSocket (packets 10047/10048)
- Integrated Color/Image tabs into BackgroundsView panel
- All strings use LocalizeText() for i18n support
- Settings persisted in localStorage + server sync with 1s debounce
- Added react-colorful dependency

src/components/room/widgets/avatar-info/infostand/InfoStandWidgetUserView.tsx

@@ -133,7 +133,7 @@ export const InfoStandWidgetUserView: FC<InfoStandWidgetUserViewProps> = props =
 
   return (
     <>
-      <Column className="relative min-w-[190px] max-w-[190px] z-30 pointer-events-auto bg-[rgba(28,28,32,0.95)] [box-shadow:inset_0_5px_#22222799,inset_0_-4px_#12121599] rounded">
+      <Column className="relative min-w-[190px] max-w-[190px] z-30 pointer-events-auto [box-shadow:inset_0_5px_#22222799,inset_0_-4px_#12121599] rounded" style={ { backgroundColor: 'var(--ui-dark-bg, rgba(28,28,32,0.95))' } }>
         <Column className="h-full p-[8px] overflow-auto" gap={1} overflow="visible">
           <div className="flex flex-col gap-1">
             <div className="flex items-center justify-between">