Update EmptyStateCta with solid background color

Update EmptyStateCta component to improve text visibility by:
- Replace transparent Card with solid primary color background
- Remove border stroke from Card
- Update text color to use onPrimary for better contrast
- Update button colors to use primaryContainer/onPrimaryContainer
- Maintain existing layout, spacing, and accessibility features

Bug: 378418098
Test: Device tested
Flag: NONE Accessibility fix
Change-Id: I0587a8a452a74481985c6f85d44f214946360661