🎨 Palette: Enhance Accessibility for Calendar View Mode Selector

[endlessblink]

💡 What: Added role="group", aria-label, and dynamically bound :aria-pressed attributes to the Calendar view mode segmented control (Day, Week, Month buttons).
🎯 Why: The view selector buttons act as a segmented toggle group. Without proper roles and :aria-pressed states, screen reader users cannot easily understand they are part of a mutually exclusive group or which mode is currently active.
♿ Accessibility: Enhanced structural semantics and exposed the active view mode state to assistive technologies.

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PR created automatically by Jules for task 406684620386376933 started by @endlessblink

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