Improve table row selection visibility and keyboard navigation

[ryanhamilton]

user-sl user-mpm

Table row and cell selection is difficult to see in dark theme.

Problems:

• Selection highlight is not visually clear
• Row selection only updates on mouse click
• Keyboard navigation (arrow keys) does not update selection state

Some users prefer keyboard navigation for speed.

Expected behavior:

• Clearer selection highlight in dark theme
• Selection updates when navigating via keyboard

Priority: HIGH