Primary action control for SterlingCraft — rust-filled by default, with bark-outline and ghost variants.

```jsx
import { Button } from "./Button.jsx";

<Button variant="primary" size="md" onClick={save}>Place order</Button>
<Button variant="secondary">View catalogue</Button>
<Button variant="ghost" iconRight={<ChevronRight />}>Learn more</Button>
```

Variants: `primary` (rust fill), `secondary` (bark outline → fills on hover), `ghost` (quiet, rust text).
Sizes: `sm` · `md` · `lg`. Props: `iconLeft`, `iconRight`, `fullWidth`, `disabled`, `href` (renders an `<a>`).
Keep labels short and sentence-case. One primary button per view.