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/app/components/ChartBuilderModal.test.tsx

@@ -24,7 +24,9 @@ vi.mock('../services/chart-renderer', () => {
     }
   }
   return {
-    renderSpec: vi.fn(() => Promise.resolve({ destroy() {}, resize() {} })),
+    renderSpec: vi.fn(() =>
+      Promise.resolve({ destroy() {}, resize() {}, inspectData: () => null }),
+    ),
     ChartTooLargeError,
   };
 });