Add Donut/Ring Progress Chart component

[yuribodo]

Description

While PieChart supports `variant: 'donut'`, a dedicated ring progress indicator (single value 0-100%) is a distinct use case for KPI dashboards — think fitness trackers, completion metrics, goal progress displays.

Features

• Single value 0-100% with smooth animation
• Customizable ring thickness
• Color gradient along the ring
• Center content (custom React node — value, icon, label)
• Multiple concentric rings for multi-metric display
• Configurable start angle

Proposed API

```tsx
<RingProgress
value={73}
max={100}
thickness={12}
color="#3b82f6"
centerContent={73%}
/>
```

Tasks

• Create `src/components/charts/ring-progress/index.tsx`
• Implement animated SVG arc with configurable thickness
• Support center content slot
• Support multiple concentric rings
• Add documentation page
• Register in CLI
• Add tests and Storybook story