Data inspector: input/resolved rows below the chart, with a resizable divider

A collapsible Data panel under the Live Preview and Chart Builder charts shows the rows the chart actually uses, switching between Input (parsed source) and Resolved (post-transform) views read from the live Vega view. Collapsed by default; the open-state and a draggable height divider persist.

Rows come through a new RenderHandle.inspectData() accessor, so no component touches the view: core/result-data picks the most-upstream source and most-downstream result from the compiled dataflow, read lazily. The divider reuses the window-splitter pattern (horizontal variant).

Consolidations: a shared DataTable primitive replaces the inspector's and the builder's duplicate read-only tables; useResizeDrag merges the col/row drag-gesture twins.

Docs: spec 04/06 and arch 05/10 updated; the now-shipped exploration memo removed.

src/main.tsx

@@ -3,8 +3,12 @@ import { App } from './app/App';
 import { initPanes, wirePanes } from './app/orchestration/panes';
 import {
   initChartTheme,
+  initDataInspectorHeight,
+  initDataInspectorOpen,
   initPreviewFitMode,
   wireChartTheme,
+  wireDataInspectorHeight,
+  wireDataInspectorOpen,
   wirePreviewFitMode,
 } from './app/orchestration/preferences';
 import { initSettings, wireSettings } from './app/orchestration/settings';
@@ -30,6 +34,10 @@ initPreviewFitMode();
 wirePreviewFitMode();
 initChartTheme();
 wireChartTheme();
+initDataInspectorOpen();
+wireDataInspectorOpen();
+initDataInspectorHeight();
+wireDataInspectorHeight();
 initPanes();
 wirePanes();