🎨 Palette: Enhance table sorting accessibility and fix semantic bug

[Woschj]

🎨 Palette: One Micro-UX Improvement

💡 What:

• Fixed a semantic HTML bug in base.html where the quickScanTrigger (a div) had a mismatched closing </button> tag.
• Enhanced the client-side table sorting in list_base.html to be fully accessible. It now supports keyboard interaction (Tab to header, Enter/Space to sort) and provides screen reader feedback via aria-sort and descriptive aria-label attributes.

🎯 Why:

• Table sorting was previously only accessible via mouse-clicks and lacked any feedback for assistive technologies.
• The tag mismatch in base.html corrupted the accessibility tree and made the sidebar navigation confusing for screen readers.

♿ Accessibility:

• Added role="button" and tabindex="0" to header wrappers.
• Implemented onkeydown for Enter and Space.
• Added aria-sort (ascending/descending) on th elements.
• Added descriptive aria-label (e.g., "Sortieren nach Name").
• Added visual focus rings for keyboard navigation.

Total change: ~35 lines of template and JS code. Verified with Playwright screenshot tests.

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PR created automatically by Jules for task 9248724336508078721 started by @Woschj

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