Refactor `PushButton` API surface for variant clarity

[GroovinChip]

According to the Sonoma Figma Kit, there are three variants of push buttons:

• primary
• secondary
• destructive

Styling Requirements:

• The background color of primary buttons should always be the system accent color or the color set in PushButtonThemeData.
• The background color of secondary buttons should always be the default white/dark grey color unless overridden by PushButtonThemeData.
• The background color of destructive buttons should always be the default white/dark grey, and the button's text should always be styled to the shade of red appropriate for current theme. Destructive buttons should not respect the background color set by PushButtonThemeData.

Implementation Steps

### Tasks
- [ ] Introduce `PushButtonVariant` enum
- [ ] Remove `color` property
- [ ] Remove `isSecondary` property
- [ ] Apply styling requirements