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.

docs/architecture/10-interaction-and-feedback.md

@@ -210,6 +210,14 @@ each above its min. **valuenow trade-off:** it reports the library's 0–100 pos
 rendered position after a window enlargement (worst near the extremes). Drag/keyboard read live
 `clientWidth`, so resizing itself stays accurate; only the announced value drifts.
 
+**Horizontal variant — the data-inspector divider.** The chart ↔ data-inspector divider in
+the Live Preview (`InspectorSplitHandle`, spec §04) is the same window-splitter contract with
+the axis flipped: `aria-orientation="horizontal"`, ↑/↓ + Home/End, sizing a stacked region's
+**height** instead of a pane's width. It reads its flanking siblings (chart above, inspector
+below) like `PaneSplitHandle`, with the gesture in `useRowResizeDrag` (the row twin of
+`useColResizeDrag`) and the clamp/value math pure in `AppStore` (`clampInspectorHeight` /
+`inspectorHeightValue`). Rendered only while the inspector is open.
+
 _(Consulted via `/council` → WAI-ARIA APG `windowsplitter`. This bullet is the contract;
 cite it, not the APG file.)_