Improve sort icon contrast to meet WCAG 3:1 ratio

Problem/Motivation

DataTables sort icons (up/down arrows in column headers) have insufficient contrast against the background, failing to meet WCAG 2.1 Level AA requirement of 3:1 contrast ratio for non-text content.

Users with low vision or in bright lighting conditions may not be able to see which columns are sortable or which direction is currently active.

Proposed resolution

Improve CSS styling for DataTables sort icons:

• Increase opacity of inactive sort indicators
• Add outline/border for active sort state
• Provide distinct hover/focus styles
• Ensure all states meet 3:1 contrast minimum

Remaining tasks

• [ ] Measure current contrast ratios
• [ ] Update CSS for sort icon states (inactive, hover, active)
• [ ] Test with contrast checking tools
• [ ] Verify across different backgrounds/themes