fix: pass urlTransform prop through to ReactMarkdown (CopilotKit#3845)

Closes CopilotKit#1921

The Markdown component accepted `components` but not `urlTransform`,
preventing users from customizing URL sanitization. Added `urlTransform`
as an optional prop with passthrough to `MemoizedReactMarkdown`.

Split from CopilotKit#3838.

Author: AlemTuzlak

.changeset/little-pears-tell.md

@@ -0,0 +1,5 @@
+---
+"@copilotkit/react-ui": patch
+---
+
+fix: pass urlTransform prop through to ReactMarkdown

packages/react-ui/src/components/chat/Markdown.tsx

@@ -126,15 +126,21 @@ const MemoizedReactMarkdown: FC<Options> = memo(
   ReactMarkdown,
   (prevProps, nextProps) =>
     prevProps.children === nextProps.children &&
-    prevProps.components === nextProps.components,
+    prevProps.components === nextProps.components &&
+    prevProps.urlTransform === nextProps.urlTransform,
 );
 
 type MarkdownProps = {
   content: string;
   components?: Components;
+  urlTransform?: Options["urlTransform"];
 };
 
-export const Markdown = ({ content, components }: MarkdownProps) => {
+export const Markdown = ({
+  content,
+  components,
+  urlTransform,
+}: MarkdownProps) => {
   const mergedComponents = useMemo(
     () => ({ ...defaultComponents, ...components }),
     [components],
@@ -148,6 +154,7 @@ export const Markdown = ({ content, components }: MarkdownProps) => {
           [remarkMath, { singleDollarTextMath: false }],
         ]}
         rehypePlugins={[rehypeRaw]}
+        {...(urlTransform !== undefined ? { urlTransform } : {})}
       >
         {content}
       </MemoizedReactMarkdown>