refactor(card): modernize composition model and improve MD3 behavior

Refactor Card to improve Material Design 3 compliance, remove problematic children patterns, improve performance characteristics, and modernize the public API.

**Problems**

- Current API relies heavily on children composition in ways that are difficult to optimize
- Internal layout logic is tightly coupled to arbitrary child structures
- MD3 behaviors and visuals are not fully aligned with current Material guidelines
- Rendering performance can degrade in large lists or frequently updated screens
- Type safety and discoverability of the API can be improved
- The component has inconsistent behavior between platforms and edge cases

**Focus Areas**

- Reduce dependence on deeply nested children
- Improve Card.Content / Card.Actions architecture
- Improve elevation and surface behavior
- Improve shape and outlined variants
- Simplify internal spacing rules

**Proposed API Direction**

Introduce clearer slot-based APIs:
`Content}
actions={[...]}
/>`

**Performance Opportunities**

- Reduce nested wrappers
- Optimize pressable behavior
- Avoid unnecessary subtree re-renders
- Improve memoization boundaries

The issue names Card, Card.Content, and Card.Actions but no file or test. Start by locating the Card implementation and its existing public API, then compare current composition, variants, elevation, spacing, and pressable behavior with the proposed slot direction; done criteria and tests are not specified, so scope needs maintainer agreement.

Written by the indexing model from the issue text.