Build a Design System / Component Library

Background: Native [platform] app, [SwiftUI / Compose]. The app will have
many screens and I want visual consistency and reusable components.
Brand basics: [colors, type, spacing, corner styles if known].

Use case: Design a small design system—tokens plus reusable
components—so screens are assembled from shared parts, not one-off
styles.

Implementation details:
- Design tokens: color, typography, spacing, radius, elevation—as named,
  centralized values (not magic numbers scattered in views)
- A starter component set: buttons (with variants/states), text fields,
  cards, list rows, loading and empty states
- iOS: ViewModifiers / style protocols / a theme in the Environment.
  Android: a Compose theme (MaterialTheme or custom) + composable
  components.
- Components must support disabled/loading/error states and be themeable
- Document usage so the system is followed, not bypassed

Layer & dependencies: A standalone UI/design-system module both feature
modules depend on.

Deliverable: The token definitions, 3–4 core components fully
implemented with their variants/states, the theming hook, and a usage
example assembling a screen from them.