perf(appkit-ui): enable tree-shaking with sideEffects flag and modular echarts imports

[MarioCadenas]

Problem (P-1, High)

@databricks/appkit-ui had no sideEffects declaration, so webpack/esbuild/Rollup consumers had to assume every module re-exported by the /react barrel (src/react/index.ts) is side-effectful and keep all of them. Importing just Button shipped the entire chart stack — including the full echarts bundle (~350KB gz), @tanstack/react-table, and marked + dompurify — because charts/base.tsx imported echarts-for-react's default entry, which imports the monolithic echarts package.

Changes

"sideEffects": ["**/*.css"] in packages/appkit-ui/package.json

This tells bundlers that only CSS files have import side effects, so any JS module whose exports are unused can be dropped from the graph. Reasoning for the array (vs false):

• No JS module in the package relies on import-time side effects from another module (no polyfills, no cross-module registration) — verified by survey. The new ECharts registration lives in the same module as BaseChart, so it always executes when any chart component is used.
• The package ships dist/styles.css (exported as ./styles.css), which consumers import purely for its side effect. Declaring false would let bundlers prune that import; ["**/*.css"] keeps it safe.
• The dist publish tool (tools/dist-appkit.ts) spreads the whole package.json, so the field survives into the published package.

Modular ECharts imports in charts/base.tsx

Switched from echarts-for-react (full echarts entry) to echarts-for-react/lib/core + echarts/core, registering exactly what the option builders in options.ts use:

• Series: LineChart (line + area), BarChart (vertical + horizontal), PieChart (pie + donut), ScatterChart, HeatmapChart, RadarChart
• Components: TitleComponent (title), TooltipComponent, LegendComponent, GridComponent (grid/xAxis/yAxis), VisualMapComponent (heatmap color scale)
• Features: LegacyGridContainLabel — the cartesian option builder sets grid.containLabel: true, which in ECharts 6 is a separately registered feature (the full bundle auto-includes it; the mount tests caught its absence as a runtime warning)
• Renderer: CanvasRenderer (BaseChart always renders with renderer: "canvas")

Nothing in options.ts/normalize.ts uses dataZoom, toolbox, markLine, dataset, or other components, so they are intentionally not registered. The ECharts instance type stays a type-only import type { ECharts } from "echarts" (erased at compile time). Consumers passing custom options that need extra features can register them in their own app via echarts/core's use() — documented in a comment at the registration site.

New mount tests (charts/__tests__/base.test.tsx)

Existing chart tests only covered pure option/normalize functions and never exercised ECharts rendering. ECharts does not throw on a missing registration — it logs "Series X is used but not imported" and renders a blank chart. The new suite mounts BaseChart for every chart family (line, area, bar, horizontal bar, scatter, pie, donut, radar, heatmap with visualMap) under jsdom with a canvas stub and fails on any missing-registration error/warning.

Verification

• pnpm build — dist preserves module structure (unbundle mode); built dist/react/charts/base.js imports only echarts/core subpaths, no bare echarts value import anywhere in dist
• pnpm vitest run --project appkit-ui — 17 files, 320 tests passed (including 9 new mount tests)
• pnpm -r typecheck, pnpm check:fix, pnpm docs:build — clean

This pull request and its description were written by Isaac.