feat: enhance playground UI

Refine the Playground's UI to improve user experience:

- Streamline chat window layout for better message readability
- Introduce a knowledge selection dropdown for easier context setting
- Improve image upload integration for a smoother workflow
- Optimize spacing and styling for a more polished visual appearance

src/components/Icons/Fireworks.tsx

@@ -12,7 +12,7 @@ export const FireworksMonoIcon = React.forwardRef<
       ref={ref}
       {...props}>
       <path
-        fill="#fff"
+        fill="#6720FF"
         d="M318.563 221.755c-17.7 0-33.584-10.508-40.357-26.777L196.549 0h47.793l74.5 178.361L393.273 0h47.793L358.92 195.048c-6.808 16.199-22.657 26.707-40.357 26.707zM425.111 314.933c-17.63 0-33.444-10.439-40.287-26.567-6.877-16.269-3.317-34.842 9.112-47.445l148.721-150.64 18.572 43.813-136.153 137.654 194.071-1.082 18.573 43.813-212.574.524-.07-.07h.035zM0 314.408l18.573-43.813 194.07 1.082L76.525 133.988l18.573-43.813 148.721 150.641c12.428 12.568 16.024 31.21 9.111 47.444-6.842 16.164-22.727 26.567-40.287 26.567L.07 314.339l-.07.069z"></path>
     </svg>
   )