Spinner: agentic color variant

import { Canvas, Controls, Meta, Title } from '@storybook/addon-docs/blocks';

import * as SpinnerStories from './Spinner.stories';

<Meta of={SpinnerStories} name='Usage' />

<Title />

## Purpose

The PDS Spinner, extended with an agentic color: `color='agentic'` paints the arc and track with the AI gradient.

`hasAvatar` adds the Zappy bolt inside the ring, in the plain foreground color (not the gradient). It is half the ring tall and shows from `2xl` up.

## Implementation

See the table below for the available props. The other stories show every variant and state.

<hr />

<Canvas of={SpinnerStories.Default} />
<Controls of={SpinnerStories.Default} />

<hr />

<Canvas of={SpinnerStories.WithIcon} />