fix(webui): keep DataGrid actions out of form submission

webui/tests/data-grid-actions.test.tsx

@@ -0,0 +1,32 @@
+function assertEqual<T>(actual: T, expected: T, message: string): void {
+  if (actual !== expected) throw new Error(`${message}: expected ${String(expected)}, got ${String(actual)}`);
+}
+
+import { renderToStaticMarkup } from "react-dom/server";
+import { DataGridEmptyAction, DataGridRowActions } from "../src/components/table/DataGrid";
+
+function noop() {}
+
+function buttonCount(markup: string): number {
+  return markup.match(/<button\b/g)?.length ?? 0;
+}
+
+function nonSubmittingButtonCount(markup: string): number {
+  return markup.match(/<button\b[^>]*\btype="button"/g)?.length ?? 0;
+}
+
+const rowActions = renderToStaticMarkup(
+  <form>
+    <DataGridRowActions onAddBelow={noop} onRemove={noop} onMoveUp={noop} onMoveDown={noop} />
+  </form>
+);
+assertEqual(buttonCount(rowActions), 4, "row actions render the expected controls");
+assertEqual(nonSubmittingButtonCount(rowActions), 4, "row actions do not submit an enclosing form");
+
+const emptyAction = renderToStaticMarkup(
+  <form>
+    <DataGridEmptyAction onAdd={noop} />
+  </form>
+);
+assertEqual(buttonCount(emptyAction), 1, "empty action renders the expected control");
+assertEqual(nonSubmittingButtonCount(emptyAction), 1, "empty action does not submit an enclosing form");