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/ShellOverlays.tsx

@@ -1,6 +1,4 @@
-import { lazy, Suspense } from 'react';
 import BashExecModal from '../BashExecModal';
-import LazyBoundary from '../LazyBoundary';
 import { PolicyBlockDialog } from '../stack/PolicyBlockDialog';
 import { UpdateReadinessDialog } from '../stack/UpdateReadinessDialog';
 import { DeleteStackDialog } from './DeleteStackDialog';
@@ -14,14 +12,6 @@ import type { OverlayState } from './hooks/useOverlayState';
 import type { StackActionsHook } from './hooks/useStackActions';
 import type { PermissionAction } from '@/context/AuthContext';
 
-// SecurityHistoryView is the only lazy-loaded view that lives outside
-// the ViewRouter switch -- it renders as an overlay sheet wired into the
-// settings flow, not as a top-level tab. The other tab-level lazy views
-// (HostConsole, FleetView, AuditLogView, etc.) live inside ViewRouter.
-const SecurityHistoryView = lazy(() =>
-  import('../SecurityHistoryView').then(m => ({ default: m.SecurityHistoryView })),
-);
-
 interface ShellOverlaysProps {
   overlayState: OverlayState;
   stackActions: StackActionsHook;
@@ -32,8 +22,6 @@ interface ShellOverlaysProps {
   stackName: string;
   gitSourceOpen: boolean;
   setGitSourceOpen: (open: boolean) => void;
-  securityHistoryOpen: boolean;
-  setSecurityHistoryOpen: (open: boolean) => void;
 }
 
 export function ShellOverlays({
@@ -46,8 +34,6 @@ export function ShellOverlays({
   stackName,
   gitSourceOpen,
   setGitSourceOpen,
-  securityHistoryOpen,
-  setSecurityHistoryOpen,
 }: ShellOverlaysProps) {
   const {
     deleteDialogOpen, closeDeleteDialog, stackToDelete,
@@ -171,21 +157,6 @@ export function ShellOverlays({
         }}
       />
 
-      {/* Scan history overlay. Conditionally mounted so the lazy chunk
-          only fetches when the user opens the overlay; an always-mounted
-          lazy component would fetch on EditorLayout's first render and
-          defeat the split. The overlay has no internal state that needs
-          to persist across opens. */}
-      {securityHistoryOpen ? (
-        <LazyBoundary>
-          <Suspense fallback={null}>
-            <SecurityHistoryView
-              open
-              onClose={() => setSecurityHistoryOpen(false)}
-            />
-          </Suspense>
-        </LazyBoundary>
-      ) : null}
     </>
   );
 }