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

package.json

@@ -21,6 +21,7 @@
         "framer-motion": "^11.2.12",
         "react": "^19.2.4",
         "react-bootstrap": "^2.10.10",
+        "react-colorful": "^5.6.1",
         "react-dom": "^19.2.4",
         "react-icons": "^5.5.0",
         "react-slider": "^2.0.6",