fix(deps): update dependency zod to v4

Author: renovate[bot]

bun.lockb

@@ -13,7 +13,7 @@
     "plainstack": "latest",
     "shiki": "^1.7.0",
     "slugify": "^1.6.6",
-    "zod": "^3.23.8"
+    "zod": "^4.0.0"
   },
   "devDependencies": {
     "@biomejs/biome": "^1.8.3",