Add UI Customization Panel with full color theming

- New "Interfaccia" panel with color picker (HSV + hex/RGB/alpha + 30 presets)
- Profile background customization tab
- Accent color propagates via CSS variables to: card headers/tabs,
  context menus, Button dark/primary/gray variants, InfoStand panels,
  toolbar, room tools, purse, .btn-primary/.btn-dark CSS classes
- All elements use var(--name, fallback) for zero visual change when default
- Settings persisted in localStorage
- Added react-colorful dependency
- Added ui-config.json with header images config keys

src/api/ui-settings/IUiSettings.ts

@@ -0,0 +1,21 @@
+export interface IUiSettings
+{
+    colorMode: 'color' | 'image' | 'default';
+    headerColor: string;
+    headerImageUrl: string;
+    headerAlpha: number;
+}
+
+export const DEFAULT_UI_SETTINGS: IUiSettings = {
+    colorMode: 'default',
+    headerColor: '#1E7295',
+    headerImageUrl: '',
+    headerAlpha: 100
+};
+
+export const PRESET_COLORS: string[] = [
+    '#000000', '#444444', '#888888', '#CCCCCC', '#660000', '#CC3333', '#FF6666', '#CC6600',
+    '#FF3333', '#FF6633', '#FF9933', '#FFCC00', '#FFFF00', '#66FF00', '#00CC00', '#009900',
+    '#00FFCC', '#33CCFF', '#3366FF', '#0000CC', '#6633CC', '#9933FF', '#CC33FF', '#FF66CC',
+    '#FF99CC', '#1E7295', '#185D79', '#2DABC2', '#2B91A7', '#283F5D'
+];