Background

This PR upgrades Graphic Walker rendering from a single built-in implementation to a plugin-based architecture, and introduces Observable Plot and ECharts as standalone renderer packages. The goals are to support extensible renderers, reduce coupling in the core package, and preserve compatibility with legacy renderer IDs.

What’s included

1) Renderer Plugin architecture (core)

• Added renderer plugin registry APIs and types in @kanaries/graphic-walker:
  • registerRendererPlugin
  • unregisterRendererPlugin
  • getRendererPlugin
  • listRendererPlugins
  • registerRendererAlias
  • resolveRendererId
• Added built-in builtin:vega plugin and auto-registration during package initialization.
• Added renderer alias compatibility: vega-lite -> builtin:vega.

2) Standalone renderer packages

• Added @kanaries/graphic-walker-renderer-observable-plot.
• Added @kanaries/graphic-walker-renderer-echarts.
• Both can be injected into GraphicRenderer or GraphicWalker via createXxxPlugin().

3) Plugin injection and fallback in rendering entry points

• GraphicRenderer / SpecRenderer / PureRenderer now accept rendererPlugins.
• Renderer selection resolves from layout.renderer; if a plugin is missing or fails canRender, it falls back to builtin:vega.
• Existing geographic rendering path (Leaflet) remains unaffected.

4) Documentation updates

• Added a Renderer Plugins section in README with examples for:
  • registerRendererPlugin(createObservablePlotPlugin())
  • registerRendererPlugin(createEChartsPlugin())
• Documented legacy renderer ID compatibility for smooth upgrades.

5) Engineering and release support

• Added renderer plugin release workflow: .github/workflows/release-renderer-plugin.yml.
• Updated playground demos with renderer switching (VegaLite / Observable Plot / ECharts).
• Enhanced chart field configuration capabilities (new field config dialog), including title override, sorting strategy, and formatting options.

Compatibility

• Existing configs with renderer: "vega-lite" continue to work.
• If a third-party plugin is not registered, charts safely fall back to builtin:vega instead of failing.

Validation

• Manually validated in playground:
  • Path: /examples/GraphicRenderer
  • Switched renderer to ECharts or Observable Plot and verified rendering works.