docs: add charts and feature documentation

content/docs/charts/index.mdx

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+---
+title: Charts
+description: Reactive ECharts bridge with lazy loading, auto-detection, and typed options for Pyreon.
+---
+
+`@pyreon/charts` provides a reactive bridge to [Apache ECharts](https://echarts.apache.org/) for Pyreon applications. Chart modules are lazy-loaded on demand -- zero bundle cost until a chart actually renders. The Canvas renderer is used by default, with SVG available as an option.
+
+<PackageBadge name="@pyreon/charts" href="/docs/charts" />
+
+## Installation
+
+```package-install
+@pyreon/charts
+```
+
+## Quick Start
+
+Use the `<Chart />` component to render a chart. Pass an options function that returns a standard ECharts configuration -- signal reads inside the function are tracked for reactivity.
+
+```tsx
+import { signal } from '@pyreon/reactivity'
+import { Chart } from '@pyreon/charts'
+
+function SalesChart() {
+  const months = signal(['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun'])
+  const revenue = signal([120, 200, 150, 80, 70, 110])
+
+  return (
+    <Chart
+      options={() => ({
+        xAxis: { type: 'category', data: months() },
+        yAxis: { type: 'value' },
+        tooltip: { trigger: 'axis' },
+        series: [{ name: 'Revenue', type: 'bar', data: revenue() }],
+      })}
+      style="height: 400px"
+    />
+  )
+}
+```
+
+The `options` prop accepts a function (not a plain object) so that signal reads are tracked. When any signal inside the function changes, the chart re-renders automatically.
+
+## API Reference
+
+### `<Chart />`
+
+The primary component for rendering charts.
+
+| Prop | Type | Description |
+|------|------|-------------|
+| `options` | `() => EChartsOption` | Function returning ECharts configuration. Signal reads are tracked for reactivity. |
+| `style` | `string` | Inline style string. Must include a height (ECharts requires a sized container). |
+| `class` | `string` | CSS class name for the container element. |
+| `renderer` | `'canvas' \| 'svg'` | Rendering mode. Defaults to `'canvas'`. |
+| `onChartReady` | `(instance: ECharts) => void` | Callback fired after the chart instance is initialized. |
+| `on*` | Event handlers | ECharts event bindings, e.g. `onClick`, `onMouseover`, `onLegendSelectChanged`. |
+
+```tsx
+<Chart
+  options={() => ({ /* ... */ })}
+  style="height: 300px"
+  renderer="svg"
+  onClick={(params) => console.log('Clicked:', params.name)}
+  onChartReady={(instance) => console.log('Chart ready:', instance)}
+/>
+```
+
+### `useChart<TOption>(optionsFn, config?)`
+
+A lower-level hook for programmatic control. Returns reactive signals for the chart instance and error state.
+
+```tsx
+import { useChart } from '@pyreon/charts'
+
+function MyChart() {
+  const { containerRef, instance, error } = useChart(() => ({
+    xAxis: { type: 'category', data: ['A', 'B', 'C'] },
+    yAxis: { type: 'value' },
+    series: [{ type: 'bar', data: [10, 20, 30] }],
+  }))
+
+  return (
+    <div>
+      {() => error() ? <p class="error">{error()!.message}</p> : null}
+      <div ref={(el) => containerRef.set(el)} style="height: 400px" />
+    </div>
+  )
+}
+```
+
+**Config options:**
+
+| Option | Type | Default | Description |
+|--------|------|---------|-------------|
+| `renderer` | `'canvas' \| 'svg'` | `'canvas'` | Rendering mode |
+| `notMerge` | `boolean` | `false` | Replace options entirely instead of merging |
+| `lazyUpdate` | `boolean` | `false` | Defer chart update to next frame |
+
+**Return value:**
+
+| Property | Type | Description |
+|----------|------|-------------|
+| `containerRef` | `Signal<HTMLElement \| null>` | Bind to a DOM element via `ref` |
+| `instance` | `Signal<ECharts \| null>` | The underlying ECharts instance (available after init) |
+| `error` | `Signal<Error \| null>` | Error signal for init or setOption failures |
+
+### Types
+
+`@pyreon/charts` re-exports all ECharts option types for strict typing:
+
+```tsx
+import type {
+  ComposeOption,
+  BarSeriesOption,
+  LineSeriesOption,
+  PieSeriesOption,
+  ScatterSeriesOption,
+  RadarSeriesOption,
+  HeatmapSeriesOption,
+  TreemapSeriesOption,
+  SankeySeriesOption,
+  GaugeSeriesOption,
+  FunnelSeriesOption,
+  CandlestickSeriesOption,
+  GraphSeriesOption,
+} from '@pyreon/charts'
+```
+
+## Auto-Detection
+
+When you provide an options function, `@pyreon/charts` inspects the configuration to determine which ECharts modules are needed:
+
+- **Series types** (`bar`, `line`, `pie`, etc.) are detected from `series[].type`
+- **Components** (`tooltip`, `legend`, `dataZoom`, etc.) are detected from top-level keys
+- **Axis types** (`category`, `value`, `time`, `log`) are detected from axis config
+
+Only the required modules are dynamically imported. A chart with `type: 'bar'` and `tooltip` will only load the bar series renderer and tooltip component -- not the full ECharts bundle.
+
+```tsx
+// Only loads: BarChart, TooltipComponent, GridComponent, CanvasRenderer
+<Chart
+  options={() => ({
+    tooltip: { trigger: 'axis' },
+    xAxis: { type: 'category', data: labels() },
+    yAxis: { type: 'value' },
+    series: [{ type: 'bar', data: values() }],
+  })}
+  style="height: 300px"
+/>
+```
+
+## Strict Typing with ComposeOption
+
+For type-safe chart configurations, use `ComposeOption<>` to narrow the options type to only the series types you use:
+
+```tsx
+import { useChart } from '@pyreon/charts'
+import type { ComposeOption, BarSeriesOption, LineSeriesOption } from '@pyreon/charts'
+
+type DashboardOption = ComposeOption<BarSeriesOption | LineSeriesOption>
+
+function Dashboard() {
+  const chart = useChart<DashboardOption>(() => ({
+    xAxis: { type: 'category', data: ['Q1', 'Q2', 'Q3', 'Q4'] },
+    yAxis: { type: 'value' },
+    series: [
+      { type: 'bar', data: [100, 200, 150, 300] },
+      { type: 'line', data: [80, 170, 130, 280] },
+    ],
+  }))
+
+  return <div ref={(el) => chart.containerRef.set(el)} style="height: 400px" />
+}
+```
+
+This gives you autocomplete and type checking for the specific series options you declared.
+
+## Manual Registration
+
+For maximum tree-shaking control, use the `@pyreon/charts/manual` entry point. This disables auto-detection and requires you to register ECharts modules explicitly:
+
+```tsx
+import { useChart, registerModules } from '@pyreon/charts/manual'
+import { BarChart, LineChart } from 'echarts/charts'
+import { TooltipComponent, GridComponent, LegendComponent } from 'echarts/components'
+import { CanvasRenderer } from 'echarts/renderers'
+
+// Register once at app startup
+registerModules([
+  BarChart,
+  LineChart,
+  TooltipComponent,
+  GridComponent,
+  LegendComponent,
+  CanvasRenderer,
+])
+
+// Then use useChart / <Chart /> as normal
+function MyChart() {
+  const chart = useChart(() => ({
+    series: [{ type: 'bar', data: [1, 2, 3] }],
+  }))
+
+  return <div ref={(el) => chart.containerRef.set(el)} style="height: 300px" />
+}
+```
+
+Use manual registration when you need deterministic bundle sizes or are building a library that should not auto-import ECharts modules.
+
+## Bundle Size
+
+| Import | Approximate Size (gzipped) |
+|--------|---------------------------|
+| `@pyreon/charts` (wrapper only) | ~2 KB |
+| + Bar chart | ~15 KB |
+| + Line chart | ~18 KB |
+| + Pie chart | ~12 KB |
+| + Tooltip + Legend | ~8 KB |
+| Full ECharts (all modules) | ~300 KB |
+
+Auto-detection ensures you only pay for what you use. A typical dashboard with 2-3 chart types loads ~40-50 KB of ECharts code.
+
+## Error Handling
+
+Both `<Chart />` and `useChart()` expose an `error` signal that captures initialization and rendering failures:
+
+```tsx
+import { Chart } from '@pyreon/charts'
+
+function SafeChart() {
+  return (
+    <Chart
+      options={() => ({
+        series: [{ type: 'bar', data: chartData() }],
+      })}
+      style="height: 300px"
+      onError={(err) => console.error('Chart error:', err)}
+    />
+  )
+}
+```
+
+With `useChart()`, check the error signal directly:
+
+```tsx
+import { useChart } from '@pyreon/charts'
+
+function SafeChart() {
+  const { containerRef, error } = useChart(() => ({
+    series: [{ type: 'bar', data: chartData() }],
+  }))
+
+  return (
+    <div>
+      {() => error() ? (
+        <div class="chart-error">
+          <p>Failed to render chart: {error()!.message}</p>
+        </div>
+      ) : null}
+      <div ref={(el) => containerRef.set(el)} style="height: 300px" />
+    </div>
+  )
+}
+```
+
+Common error scenarios:
+- Container element has zero height (ECharts requires a sized container)
+- Invalid option structure passed to `setOption`
+- Network failure when lazy-loading ECharts modules