Don't show validation message for Selects immediately

From https://github.com/getodk/web-forms/pull/164#issuecomment-2297309308:

> It would be good if select constraint messages don’t show up on first selection if user hasn’t moved on. Inputs use blur. It would require a little more logic to produce a similar experience for selects as radios/checkboxes (e.g. some delay on blur to cancel on interaction with additional items)

Review the discussion in pull request 164 and trace the select constraint-validation flow, comparing it with the blur behavior for inputs and interaction handling for radios or checkboxes. Done means a select constraint message does not appear on the first selection before the user moves on, while later validation still works.

Written by the indexing model from the issue text.