build(webapp): add @types/node so vite.config typechecks standalone

vite.config.ts uses node APIs (node:path, process, __dirname); @types/node
was only present transitively via the monorepo root. Declare it on the
webapp so the standalone Docker build's tsc -b passes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Wieedze

packages/webapp/package.json

@@ -21,6 +21,7 @@
     "wagmi": "^2.12.0"
   },
   "devDependencies": {
+    "@types/node": "^20.0.0",
     "@types/react": "^18.3.3",
     "@types/react-dom": "^18.3.0",
     "@types/three": "^0.169.0",