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/examples/index.ts

@@ -1,12 +1,13 @@
 // Sample data and ready-made example cards. Everything here is illustrative, not business data.
 export { sampleBar, sampleLine, sampleDonut, sampleDonutStates, sampleHorizontalBar, sampleSignedBar, sampleLineCompare, sampleLinePointColors, sampleDataNotice } from "./sample-data"
-export { BarChartExample, StackedBarChartExample, HorizontalBarChartExample, SignedBarChartExample, LineChartExample, LineCurveExample, LineCurveDotLabelExample, LineStraightExample, LineStraightColorLabelExample, LineStepExample, LineStepDotLabelExample, DonutChartExample, DonutPlainExample, DonutCenterExample, DonutActiveExample, DonutInteractiveExample, ChartExamples, SampleDataBadge } from "./chart-examples"
+export { BarChartExample, StackedBarChartExample, HorizontalBarChartExample, SignedBarChartExample, LineChartExample, LineCurveExample, LineCurveDotLabelExample, LineStraightExample, LineStraightColorLabelExample, LineStepExample, LineStepDotLabelExample, DonutChartExample, DonutPlainExample, DonutCenterExample, DonutSolidExample, DonutActiveExample, DonutInteractiveExample, ChartExamples, SampleDataBadge } from "./chart-examples"
 export { samplePie, sampleStackedPie, sampleRadar } from "./sample-data"
 export {
   PiePlainExample,
   PieLabelExample,
   PieLabelListExample,
   PieStackedExample,
+  PieSolidExample,
   RadarPlainExample,
   RadarDotExample,
   RadarLinesOnlyExample,