Improve validation on modules (remove `shinyvalidate` dependency)

It is true, indeed it is a long, harcoded validation that won't be easy to generalize and to remove. We might create an issue to refactor and leave it for later

_Originally posted by @osenan in https://github.com/insightsengineering/teal.goshawk/pull/378#discussion_r3803390372_

No files or tests are named. Start by tracing validation in the modules and locating the shinyvalidate dependency, then determine how the current hardcoded validation is structured. Done should mean the validation is improved and shinyvalidate is no longer required, but the generalization scope needs clarification first.

Written by the indexing model from the issue text.