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/context-menu/ContextMenuView.tsx

@@ -76,7 +76,6 @@ export const ContextMenuView: FC<ContextMenuViewProps> = ({
   const getClassNames = useMemo(() => {
     const classes = [
       'p-[2px]!',
-      'bg-[#1c323f]',
       'border-2',
       'border-[solid]',
       'border-[rgba(255,255,255,.5)]',
@@ -98,6 +97,7 @@ export const ContextMenuView: FC<ContextMenuViewProps> = ({
       top: pos.y ?? 0,
       transition: isFading ? 'opacity 75ms linear' : undefined,
       opacity,
+      backgroundColor: 'var(--ui-ctx-bg, #1c323f)',
       ...style,
     }),
     [pos, opacity, isFading, style]