feat(chart): add @hm-design/chart package with Bar, Line, Donut, Pie, Radar, Area and Radial charts

- new workspace package packages/chart (shadcn/ui Chart + Recharts, HM Theme tokens), examples entry with sample data
- Storybook Chart group (src/chart), consumer example (examples/chart), build:chart / build:chart-example scripts
- README rewritten as the AI usage guide (install, CSS wiring, chart selection, data rules, verification)
- docs: package count/list, Submodule guide (chart workspace, React dedupe), shared AI_GUIDE row, MAINTAINING, story inventory

packages/chart/src/components/series.ts

@@ -0,0 +1,44 @@
+import type { ChartConfig } from "./chart"
+
+/** HM series colors. They resolve to existing HM palette tokens (see chart.css), never to HEX values. */
+export const chartColors = [
+  "var(--hm-chart-1)",
+  "var(--hm-chart-2)",
+  "var(--hm-chart-3)",
+  "var(--hm-chart-4)",
+  "var(--hm-chart-5)",
+] as const
+
+/** Light end of each HM series color (stacked bar segments): the same palette family, lighter (see chart.css). */
+export const chartLightColors = [
+  "var(--hm-chart-1-light)",
+  "var(--hm-chart-2-light)",
+  "var(--hm-chart-3-light)",
+  "var(--hm-chart-4-light)",
+  "var(--hm-chart-5-light)",
+] as const
+
+/** One data series. `key` becomes a CSS variable name (`--color-<key>`), so use letters, digits, `-` or `_` only. */
+export type ChartSeries = {
+  key: string
+  label: string
+  /** Any CSS color. Defaults to the HM series color for the series position. */
+  color?: string
+  /** Light end of a stacked bar segment (any CSS color). Defaults to the HM light color of the series position.
+   * A series with a custom `color` and no `lightColor` is drawn as a flat segment. */
+  lightColor?: string
+}
+
+export function seriesColor(index: number, color?: string) {
+  return color ?? chartColors[index % chartColors.length]
+}
+
+export function seriesLightColor(index: number, color?: string, lightColor?: string) {
+  return lightColor ?? color ?? chartLightColors[index % chartLightColors.length]
+}
+
+export function seriesToConfig(series: readonly ChartSeries[]): ChartConfig {
+  return Object.fromEntries(
+    series.map((item, index) => [item.key, { label: item.label, color: seriesColor(index, item.color) }]),
+  )
+}