🔄 refactor: Migrate to react-resizable-panels v4 with Artifacts Header polish (#12356)

* chore: Update react-resizable-panels dependency to version 4.7.4

- Upgraded the "react-resizable-panels" package in package-lock.json, package.json, and client package.json files to ensure compatibility with the latest features and improvements.
- Adjusted peer dependencies for React and ReactDOM to align with the new version requirements.

* refactor: Update Share and SidePanel components to `react-resizable-panels` v4

- Refactored the ShareArtifactsContainer to utilize a new layout change handler, enhancing artifact panel resizing functionality.
- Updated ArtifactsPanel to use the new `usePanelRef` hook, improving panel reference management.
- Simplified SidePanelGroup by removing unnecessary layout normalization and integrating default layout handling with localStorage.
- Removed the deprecated `normalizeLayout` utility function to streamline the codebase.
- Adjusted Resizable components to ensure consistent sizing and layout behavior across panels.

* style: Enhance scrollbar appearance across application

- Added custom scrollbar styles to both artifacts and markdown files, improving aesthetics and user experience.
- Implemented dark mode adjustments for scrollbar visibility, ensuring consistency across different color schemes.

* style: Standardize button sizes and layout in Artifacts components

- Updated button dimensions to a consistent height of 9 units across various components including Artifacts, Code, and DownloadArtifact.
- Adjusted padding and layout properties in the Artifacts header for improved visual consistency.
- Enhanced the Radio component to accept a new `buttonClassName` prop for better customization of button styles.

* chore: import order

client/src/utils/index.ts

@@ -113,24 +113,6 @@ export const extractContent = (
   return '';
 };
 
-export const normalizeLayout = (layout: number[]) => {
-  const sum = layout.reduce((acc, size) => acc + size, 0);
-  if (Math.abs(sum - 100) < 0.01) {
-    return layout.map((size) => Number(size.toFixed(2)));
-  }
-
-  const factor = 100 / sum;
-  const normalizedLayout = layout.map((size) => Number((size * factor).toFixed(2)));
-
-  const adjustedSum = normalizedLayout.reduce(
-    (acc, size, index) => (index === layout.length - 1 ? acc : acc + size),
-    0,
-  );
-  normalizedLayout[normalizedLayout.length - 1] = Number((100 - adjustedSum).toFixed(2));
-
-  return normalizedLayout;
-};
-
 export const handleUIAction = async (result: UIActionResult, ask: TAskFunction) => {
   const supportedTypes = ['intent', 'tool', 'prompt'];