chore(backend): bump zod from 3.25.76 to 4.0.5 in /services/backend

Bumps [zod](https://github.com/colinhacks/zod) from 3.25.76 to 4.0.5.
- [Release notes](https://github.com/colinhacks/zod/releases)
- [Commits](colinhacks/zod@v3.25.76...v4.0.5)

---
updated-dependencies:
- dependency-name: zod
  dependency-version: 4.0.5
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

services/backend/package.json

@@ -38,7 +38,7 @@
     "pino": "^9.7.0",
     "pino-pretty": "^13.0.0",
     "pug": "^3.0.2",
-    "zod": "^3.25.76",
+    "zod": "^4.0.5",
     "zod-to-json-schema": "^3.24.6"
   },
   "devDependencies": {