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.module.css

@@ -355,44 +355,8 @@
   color: var(--text-placeholder);
 }
 
-.previewTableWrap {
-  max-height: 200px;
-  overflow: auto;
-  border: var(--border-width) solid var(--border);
-  border-radius: var(--radius);
-}
-
-.previewTableWrap:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: -1px;
-}
-
-.previewTable {
-  border-collapse: collapse;
-  width: 100%;
-  font-family: var(--font-mono);
-  font-size: 11px;
-  line-height: 1.4;
-}
-
-.previewTable th,
-.previewTable td {
-  text-align: left;
-  padding: var(--space-1) var(--space-2);
-  border-bottom: var(--border-width) solid var(--border);
-  white-space: nowrap;
-  max-width: 180px;
-  overflow: hidden;
-  text-overflow: ellipsis;
-}
-
-.previewTable thead th {
-  position: sticky;
-  top: 0;
-  z-index: 1;
-  background: var(--layer-01);
-}
-
+/* The per-column type chip in the source-preview header (the table structure and
+   cell styling now live in the shared DataTable). */
 .previewColName {
   font-weight: 600;
   color: var(--text-secondary);
@@ -403,10 +367,6 @@
   font-weight: 400;
 }
 
-.previewTable tbody tr:last-child td {
-  border-bottom: none;
-}
-
 .previewEmptyNote {
   margin: 0;
   font-size: 11px;