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

tsconfig.json

@@ -34,7 +34,7 @@
     "allowSyntheticDefaultImports": true,
     "isolatedModules": true,
     // Language and Environment
-    "jsx": "preserve",
+    "jsx": "react-jsx",
     "jsxImportSource": "@emotion/react",
     "lib": ["ESNext", "DOM"],
     "target": "ES2022",