fix(deps): update dependency zod to v4

Author: renovate[bot]

plugins/promptfoo/package-lock.json

@@ -15,7 +15,7 @@
     "discover": "node --env-file=.env dist/cli.js"
   },
   "dependencies": {
-    "zod": "^3.24.0",
+    "zod": "^4.0.0",
     "yaml": "^2.7.0",
     "ws": "^8.18.0"
   },