Clinet API Request validator

I think we need a validator for request of client api handlers.

- https://github.com/go-playground/validator
- https://github.com/asaskevich/govalidator

Start by locating the client API handlers and reviewing how their requests are currently processed. Compare the validator libraries linked in the issue, then clarify which request fields and validation failures must be covered before implementation; the issue does not name files, tests, or acceptance criteria.

Written by the indexing model from the issue text.