Use pnpm and more clean-up of sandbox mode

package.json

@@ -67,7 +67,6 @@
     "@ai-sdk/google": "^1.2.10",
     "@ai-sdk/openai": "^1.3.7",
     "@biomejs/biome": "^1.9.4",
-    "@codesandbox/sandpack-client": "^2.19.8",
     "@monaco-editor/react": "^4.7.0-rc.0",
     "@openrouter/ai-sdk-provider": "^0.4.5",
     "@radix-ui/react-accordion": "^1.2.4",
@@ -120,4 +119,4 @@
     "update-electron-app": "^3.1.1",
     "uuid": "^11.1.0"
   }
-}
+}