Add Section 508 accessibility compliance for weekly day selection

This commit completes the 508 accessibility compliance work by adding
aria-labels to weekly day selection buttons, providing full weekday names
for screen readers. This builds upon existing accessibility features that
were previously ported from the original recurring_select project:

- Focus trapping within modal dialog
- Aria-labels for calendar day/month links
- Enhanced color contrast ratios (WCAG compliant)
- Title attributes on interval inputs
- Keyboard-accessible links with href attributes

Credit to @iamanissa for the original 508 compliance work in
gregschmit/recurring_select PR gregschmit#130.

Co-Authored-By: iamanissa <iamanissa@users.noreply.github.com>

Author: saturnflyer

app/assets/javascripts/ice_cube_select_dialog.js

@@ -518,7 +518,8 @@
       let dayButtons = '';
       for (let d = firstDay; d < firstDay + 7; d++) {
         const dayOfWeek = d % 7;
-        dayButtons += `<a href="#" data-value="${dayOfWeek}">${texts.days_first_letter[dayOfWeek]}</a>`;
+        const fullDayName = this.fullStringWeekday(dayOfWeek);
+        dayButtons += `<a href="#" data-value="${dayOfWeek}" aria-label="${fullDayName}">${texts.days_first_letter[dayOfWeek]}</a>`;
       }
 
       return `