fix: replace `@finom/zod-to-json-schema` with `zod-v3-to-json-schema`

`@finom/zod-to-json-schema` is deprecated, see this comment: https://github.com/StefanTerdell/zod-to-json-schema/issues/178#issuecomment-3533122539 Deprecation warning: <img width="594" height="101" alt="image" src="https://github.com/user-attachments/assets/ee23efca-8356-424f-8e74-34b2273eeab2" />