feat(chart): add solid (thick) pie and donut charts

Add HMSolidPieChart and HMSolidDonutChart: a tilted, SVG-drawn disc with an
outer wall and, for the donut, an inner wall seen through the hole. Same data,
slice angles, order, legend and tooltip as the 2D charts; the tooltip is the
same on the top face and the walls and follows the pointer. The existing 2D
charts and their props are unchanged.

- Side walls use darker HM tokens (--hm-chart-1-side .. --hm-chart-5-side) and
  a color-mix darkening for custom colors; shared chart tokens are untouched.
- Add a "입체형" example to the Pie Chart and Donut Chart stories
  (PieSolidExample, DonutSolidExample); ExampleCard description is now optional.
- Document usage and constraints in the chart package README.

packages/chart/src/index.ts

@@ -27,6 +27,8 @@ export type { ChartSeries } from "./components/series"
 
 export { HMPieChart, HMStackedPieChart } from "./components/pie-chart"
 export type { HMPieChartProps, HMPieRing, HMStackedPieChartProps } from "./components/pie-chart"
+export { HMSolidPieChart, HMSolidDonutChart } from "./components/solid-chart"
+export type { HMSolidPieChartProps, HMSolidDonutChartProps } from "./components/solid-chart"
 export { HMRadarChart } from "./components/radar-chart"
 export type { HMRadarChartProps } from "./components/radar-chart"
 export { HMAreaChart } from "./components/area-chart"