fix(core): add @types/node as explicit dev dependency

Fixes CI build failure where ChildProcess.on() was unresolved due to
@types/node only being available transitively.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: cevian

packages/core/package.json

@@ -64,6 +64,7 @@
     "@nangohq/frontend": "^0.69.43",
     "@tailwindcss/vite": "^4.2.1",
     "@types/express": "^5.0.6",
+    "@types/node": "^22.19.15",
     "@types/pg": "^8.18.0",
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",