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/apps/electron/package.json

@@ -59,8 +59,8 @@
     "glob": "^11.0.0",
     "lodash-es": "^4.17.21",
     "nanoid": "^5.0.7",
-    "react": "^18.2.0",
-    "react-dom": "^18.2.0",
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0",
     "react-router-dom": "^6.22.3",
     "rxjs": "^7.8.1",
     "semver": "^7.6.0",