feat: chart-led Security overview with sortable Images and History tables (#1364)

* feat: chart-led Security overview with sortable Images and History tables

Refine the Security page around the existing design system and add the
data the dashboard needs.

- Overview leads with four charts (30-day risk trend, severity donut, top
  exposed images, findings by type); the signal-rail counts become a
  secondary summary, and the scanner and deploy-enforcement posture follow.
- Images becomes a recessed table with search, a severity filter, sortable
  columns, a last-scan column, and inline scan actions; the findings cell is
  clickable into the scan sheet, and the per-row cursor tooltip is dropped
  where the columns already carry that information.
- Policies puts deploy-enforcement first, collapses the policy packs into an
  accordion, and uses the standard primary button for Add policy.
- Suppressions and acknowledgements move their titles and Add buttons outside
  the cards, matching the Fleet tab layout.
- History switches from the detail sheet to an inline table (search, sortable
  columns, two-scan compare, pagination); the now-unreachable scan-history
  overlay is removed.
- Add GET /api/security/overview/trend, a node-scoped daily critical/high
  rollup backing the risk-trend chart.
- Extract the shared image-scan hook and the severity classifier, and harden
  the overview data fetch so a malformed non-critical response can never read
  as a clean security state.

* fix: treat malformed Security responses as errors, not empty or clean states

Address an independent review of the data-fetch paths so a 200 with an
unexpected shape can never read as a benign "no findings" view.

- SecurityView: validate that the image-summaries body is a scan-summary map; an
  unexpected shape now sets the error state instead of an empty map. Isolate the
  trend fetch in its own self-catching promise so a transport failure on the
  non-critical chart can no longer poison the overview or summaries error state.
- useImageScan: only a "completed" poll counts as success (a malformed or unknown
  status now throws), and a failed post-scan summaries refresh is logged instead
  of silently dropped.
- HistoryTab: a 200 whose body lacks an items array is treated as an error, not
  an empty "no completed scans" list.

frontend/src/components/EditorLayout/__tests__/useViewNavigationState.test.tsx

@@ -58,7 +58,6 @@ describe('useViewNavigationState', () => {
     const { result } = renderHook(() => useViewNavigationState());
     expect(result.current.activeView).toBe('dashboard');
     expect(result.current.settingsSection).toBe('appearance');
-    expect(result.current.securityHistoryOpen).toBe(false);
     expect(result.current.filterNodeId).toBeNull();
     expect(result.current.schedulePrefill).toBeNull();
     expect(result.current.mobileNavOpen).toBe(false);
@@ -156,18 +155,6 @@ describe('useViewNavigationState', () => {
     expect(result.current.filterNodeId).toBe(5);
   });
 
-  it('SENCHO_NAVIGATE_EVENT with security-history opens the sheet without changing activeView', () => {
-    const { result } = renderHook(() => useViewNavigationState());
-    act(() => {
-      window.dispatchEvent(
-        new CustomEvent(SENCHO_NAVIGATE_EVENT, { detail: { view: 'security-history', nodeId: 3 } }),
-      );
-    });
-    expect(result.current.securityHistoryOpen).toBe(true);
-    expect(result.current.filterNodeId).toBe(3);
-    expect(result.current.activeView).toBe('dashboard');
-  });
-
   it('SENCHO_NAVIGATE_EVENT with no nodeId sets filterNodeId to null', () => {
     const { result } = renderHook(() => useViewNavigationState());
     act(() => {