fix(core): add null checks for timeout refs and event listeners for React 19 compatibility (#9116)

## Description
- Add null checks before clearTimeout calls in colorful-fallback.tsx, edgeless.dialog.tsx, and local.dialog.tsx
- Fix event listener cleanup in unfolding.tsx
- Update tsconfig.jsx to use react-jsx transform

## Testing
- [x] Verified type safety improvements for React 19 compatibility
- [x] Ensured proper cleanup of event listeners and timeouts
- [x] Confirmed no unintended side effects from the changes

Link to Devin run: https://app.devin.ai/sessions/2e790f3ea0d84402837ec6c3c6f83e4c

packages/frontend/component/src/ui/avatar/colorful-fallback.tsx

@@ -1,5 +1,5 @@
 import clsx from 'clsx';
-import { useMemo, useRef, useState } from 'react';
+import { useEffect, useMemo, useRef, useState } from 'react';
 
 import {
   DefaultAvatarBottomItemStyle,
@@ -27,11 +27,15 @@ export const ColorfulFallback = ({ char }: { char: string }) => {
     return colorsSchema[index % colorsSchema.length];
   }, [char]);
 
-  const timer = useRef<ReturnType<typeof setTimeout>>();
+  const timer = useRef<ReturnType<typeof setTimeout> | null>(null);
 
   const [topColor, middleColor, bottomColor] = colors;
   const [isHover, setIsHover] = useState(false);
 
+  useEffect(() => {
+    return () => void (timer.current && clearTimeout(timer.current));
+  }, []);
+
   return (
     <div
       className={DefaultAvatarContainerStyle}
@@ -41,7 +45,9 @@ export const ColorfulFallback = ({ char }: { char: string }) => {
         }, 300);
       }}
       onMouseLeave={() => {
-        clearTimeout(timer.current);
+        if (timer.current) {
+          clearTimeout(timer.current);
+        }
         setIsHover(false);
       }}
     >