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/chart.css

@@ -17,6 +17,13 @@
   --hm-chart-4-light: var(--hm-sem-palette-brown-light-4);
   --hm-chart-5-light: var(--hm-sem-palette-warm-neutral-light);
 
+  /* Side walls of the solid (thick) pie and donut: the next palette step darker in the same family as the series color. */
+  --hm-chart-1-side: var(--hm-sem-palette-green-light-1);
+  --hm-chart-2-side: var(--hm-sem-palette-brown-light-1);
+  --hm-chart-3-side: var(--hm-sem-palette-green-light-2);
+  --hm-chart-4-side: var(--hm-sem-palette-brown-light-3);
+  --hm-chart-5-side: var(--hm-sem-palette-warm-neutral-dark);
+
   --hm-chart-tooltip-background: var(--hm-sem-bg-surface);
   --hm-chart-tooltip-border-color: var(--hm-sem-stroke-default);
   --hm-chart-tooltip-radius: var(--hm-radius-container);