🎨 Palette: Accessibility and Interaction improvements for QuickScan and Search

[Woschj]

This PR introduces a series of micro-UX and accessibility improvements focused on the QuickScan workflow and global navigation.

💡 What:

• QuickScan Accessibility: The "item" and "worker" cards now function correctly for keyboard users (role="button", tabindex="0", Enter/Space support). Focus indicators were added for better visibility.
• Async Feedback: The QuickScan confirmation button now shows a loading spinner and "Verarbeitung..." text while processing, preventing multiple submissions and providing clear feedback.
• Global A11y: Added missing aria-label attributes to the department dropdown, search inputs, and search buttons across the application.
• Semantic HTML: Icon-only buttons (like the close button in modals) now correctly hide their purely decorative or symbolic icons from screen readers using aria-hidden.

🎯 Why:

• These changes ensure the application is accessible to users relying on screen readers or keyboard navigation.
• Providing visual feedback for asynchronous operations makes the interface feel more responsive and reliable.

♿ Accessibility:

• Verified aria-label, role, and tabindex properties using Playwright.
• Ensured focus management and keyboard interaction support.

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PR created automatically by Jules for task 7324296508960947606 started by @Woschj

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