fix: replace color-inversion hover with subtle scale and highlight #37

Bug

Hovering over table rows and submission cards inverts colors, making text difficult to read.

Expected Behavior

Hover should enhance readability. Use subtle scale-up and light background highlight instead of full color inversion.

Acceptance Criteria

• Table rows highlight with light gray background on hover, no color inversion
• Submission cards scale up slightly on hover with subtle border emphasis
• Pipeline stages use subtle highlight on hover
• All hover states remain readable with good contrast

Out of Scope

• Dark mode adjustments (separate issue)