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/LivePreview.test.tsx

@@ -27,6 +27,10 @@ const H = vi.hoisted(() => ({
   pending: [] as Array<() => void>,
   destroyed: [] as number[],
   configs: [] as unknown[],
+  inspected: null as {
+    input: ReadonlyArray<Record<string, unknown>>;
+    resolved: ReadonlyArray<Record<string, unknown>>;
+  } | null,
 }));
 vi.mock('../services/chart-renderer', () => ({
   renderSpec: (node: HTMLElement, _spec: unknown, config: unknown) => {
@@ -44,6 +48,7 @@ vi.mock('../services/chart-renderer', () => ({
             H.destroyed.push(id);
           },
           resize() {},
+          inspectData: () => H.inspected,
         });
       });
     });