fix(review-gates): green success badges, null-safe preview rows, optional section items

- Extract shared statusBadgeClass() helper (src/viewers/statusBadge.ts) so
  SqlViewer, CteResultViewer and PhaseSummaryViewer can't drift: ok/success/
  passed/promoted render green (--success), warn renders amber (--warning),
  error/failed stay destructive red, everything else stays neutral outline.
  Previously CteResultViewer/PhaseSummaryViewer mapped "ok"/"promoted" to the
  default badge variant, which is bg-primary (GSD red) — success states
  rendered red.
- enrich.js: buildCteResultV2 now falls back preview.rows to [] instead of
  null when last_test.preview_rows is missing (pre-upgrade ok records), and
  CteResultViewer reads result.preview?.rows?.length with a null-safe
  fallback so it degrades to the "No preview rows" empty state instead of
  crashing.
- PhaseSummaryViewer: section.items is optional (model-authored sections can
  be prose-only); render (section.items ?? []) instead of crashing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/viewers/CteResultViewer.test.tsx

@@ -76,6 +76,16 @@ test("shows empty-state when preview has no rows", async () => {
   expect(screen.getByText(/no preview rows/i)).toBeInTheDocument();
 });
 
+test("shows empty-state, no crash, when preview.rows is null (pre-upgrade records)", async () => {
+  const nullRows = {
+    ...okResult,
+    preview: { columns: ["paziente_id"], rows: null as unknown as (string | number)[][] },
+  };
+  render(<CteResultViewer result={nullRows} />);
+  await screen.findByTestId("hl");
+  expect(screen.getByText(/no preview rows/i)).toBeInTheDocument();
+});
+
 test("renders columns definition list with descriptions", async () => {
   const { container } = render(<CteResultViewer result={okResult} />);
   await screen.findByTestId("hl");