chore: add react-resizable-panels

Author: joshunrau

apps/playground/package.json

@@ -39,6 +39,7 @@
     "react-dom": "workspace:react-dom__19.x@*",
     "react-dropzone": "^14.3.8",
     "react-error-boundary": "^5.0.0",
+    "react-resizable-panels": "^2.1.7",
     "stacktrace-parser": "^0.1.11",
     "ts-pattern": "workspace:ts-pattern__5.x@*",
     "zod": "workspace:zod__3.x@*",