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/PhaseSummaryViewer.test.tsx

@@ -81,6 +81,16 @@ test("renders open_questions as a bullet list", () => {
   expect(screen.getByText("Serve confermare la finestra temporale?")).toBeInTheDocument();
 });
 
+test("renders a section with title only (no items key) without crashing", () => {
+  const proseOnly: PhaseSummaryV2 = {
+    schema_version: 2,
+    phase: { id: "F5", num: 5, name: "sintesi" },
+    sections: [{ title: "Note libere" }],
+  };
+  render(<PhaseSummaryViewer phase={proseOnly} />);
+  expect(screen.getByText("Note libere")).toBeInTheDocument();
+});
+
 test("omits open_questions section when empty and shows no 'undefined' text", () => {
   const minimal: PhaseSummaryV2 = {
     schema_version: 2,