Visibility feature tweaks

[fbacall]

Summary of changes

• Allow event/material visibility checkbox to be disabled
• Display the hint at all times, without requiring hover
• I18n

Motivation and context

A user wasn't clear about what the checkbox does, and it is the first thing you see on the new event form

Checklist

• I have read and followed the CONTRIBUTING guide.
• I confirm that I have the authority necessary to make this contribution on behalf of its copyright owner and agree
  to license it to the TeSS codebase under the
  BSD license.

[Copilot]

Pull Request Overview

This PR refines the visibility feature for events and materials by updating locale strings and conditionally rendering the visibility checkbox input based on a configuration flag.

• Updated i18n content in en.yml to improve clarity about visibility.
• Modified both event and material form views to display the hint at all times and conditionally render the visibility input.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
config/locales/en.yml	Revised locale strings for better clarity in event/material visibility settings.
app/views/materials/_form.html.erb	Updated conditional rendering for the visibility checkbox using hint text.
app/views/events/_form.html.erb	Updated conditional rendering for the visibility checkbox using hint text.