🎨 Palette: Improve accessibility of icon-only buttons

[endlessblink]

💡 What: Added aria-label attributes to various icon-only buttons and contextual action buttons across multiple components (CanvasContextMenu, UnifiedInboxList, MiniCanvasToolbar, and TaskList). Also implemented dynamic aria-label and aria-pressed attributes for the completed subtasks toggle button in MiniCanvasToolbar.vue, and fixed a duplicate aria-label in SidebarHeader.vue.

🎯 Why: To improve the accessibility of the application. Icon-only buttons without proper ARIA labels are inaccessible to screen readers, making it impossible for visually impaired users to understand the purpose of the buttons.

♿ Accessibility: Ensures that all modified icon buttons and interactive toggles are now correctly announced by screen readers, adhering to WCAG guidelines for non-text content.

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PR created automatically by Jules for task 4743804270313941398 started by @endlessblink

[google-labs-jules]

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