feat: add dedicated Security page and policy-pack foundation (#1362)

* feat: add dedicated Security page and policy-pack foundation

Bring vulnerability scanning, scan history, suppressions, Compose risks,
secrets, policy packs, and scanner setup into one node-scoped Security
command center instead of scattering them across Resources and Settings.

- New top-level Security view with Overview, Images, Compose risks,
  Secrets, Policies, Suppressions, History, and Scanner setup tabs
  (status masthead + signal rail; controlled tabs with deep-link support).
- Backend: GET /security/overview rollup and GET /security/policy-packs
  static catalog (auth-only, Community). DatabaseService gains an uncapped
  scan-status count and a node-eligible block-policy count, and
  getImageScanSummaries now projects secret and misconfig counts.
- Reuse existing surfaces: the scan-history sheet, the control-governed
  suppression and acknowledgement panels, and the scan-detail sheet (now
  with an initial-tab prop so it opens on the matching finding type).
- Extract a shared SeverityBadge (from Resources) and a TrivyManager
  (from Settings) so both surfaces render identical controls.
- Resources "Scan history" now links into the Security page History tab.
- Docs for the new Security surface and tests for the new endpoints,
  helpers, nav wiring, and tabs.

* refactor: consolidate scanner and policy management onto the Security page

Remove the Settings "Vulnerability Scanning" section now that the Security
page covers the same ground, with every option preserved:

- Scanner install / update / uninstall / auto-update live on the Scanner setup
  tab (TrivyManager).
- Scan policies, the honor-suppressions toggle, and the replica
  managed-by-control / demote controls move into a new ScanPolicyManager on the
  Policies tab (paid; Community sees only the policy-pack catalog).
- CVE suppressions and acknowledgements remain on the Suppressions tab.

Wiring removed: the registry section and the now-empty Security settings group,
the SectionId, the SettingsSectionContent case and the isPaid prop it was the
sole consumer of, and SecuritySection itself. The dashboard configuration-status
"Vulnerability scanning" row now navigates to the Security page Policies tab.

Docs that pointed at "Settings -> Security -> Vulnerability Scanning" are swept
to the relevant Security page tabs.

* fix: harden Security page scanner refresh, policy-load errors, and secret-only badges

Address independent-review findings on the Security page:

- Scanner setup now refreshes Trivy state when the active node changes, so the
  displayed scanner status matches the node TrivyManager's actions target (both
  follow x-node-id). Previously, switching nodes on the tab left stale state.
- ScanPolicyManager surfaces an explicit error state on a failed policy fetch
  instead of falling through to a false "No scan policies configured".
- The shared SeverityBadge and the Images findings column no longer label a scan
  "clean" when it has secrets or misconfigurations but no CVE severity
  (highest_severity is derived from vulnerabilities only); they show a "Findings"
  state and the secret/misconfig counts instead.
- The Overview enforcement note points to the Policies tab, not the removed
  Settings section.
- The History tab auto-opens the scan-history sheet only on a deep-link (mount
  with the History tab active), not on every manual tab selection.

Adds tests for the badge secret/misconfig state and the policy-load error state.

frontend/src/components/ui/__tests__/SeverityBadge.test.tsx

@@ -0,0 +1,53 @@
+/**
+ * The severity badge was extracted from ResourcesView into a shared component so
+ * Resources and the Security page render an identical pill. Lock its label
+ * mapping (highest severity, or "Clean" when there are no findings).
+ */
+import { it, expect, vi } from 'vitest';
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { SeverityBadge } from '../SeverityBadge';
+import type { ScanSummary } from '@/types/security';
+
+function summary(overrides: Partial<ScanSummary>): ScanSummary {
+  return {
+    image_ref: 'nginx:1',
+    highest_severity: 'CRITICAL',
+    scanned_at: 1,
+    scan_id: 1,
+    total: 0,
+    critical: 0,
+    high: 0,
+    medium: 0,
+    low: 0,
+    unknown: 0,
+    fixable: 0,
+    secret_count: 0,
+    misconfig_count: 0,
+    ...overrides,
+  };
+}
+
+it('renders the highest severity and fires onClick', async () => {
+  const onClick = vi.fn();
+  render(<SeverityBadge summary={summary({ highest_severity: 'CRITICAL', total: 5, critical: 5 })} onClick={onClick} />);
+  const btn = screen.getByRole('button', { name: /CRITICAL/ });
+  await userEvent.click(btn);
+  expect(onClick).toHaveBeenCalledOnce();
+});
+
+it('renders "Clean" when there are no findings of any kind', () => {
+  render(<SeverityBadge summary={summary({ highest_severity: null })} onClick={() => {}} />);
+  expect(screen.getByRole('button', { name: /Clean/ })).toBeInTheDocument();
+});
+
+it('renders "Findings" (not "Clean") for a secret-only scan with no CVE severity', () => {
+  render(<SeverityBadge summary={summary({ highest_severity: null, secret_count: 2 })} onClick={() => {}} />);
+  expect(screen.getByRole('button', { name: /Findings/ })).toBeInTheDocument();
+  expect(screen.queryByRole('button', { name: /Clean/ })).not.toBeInTheDocument();
+});
+
+it('renders "Findings" for a misconfig-only scan', () => {
+  render(<SeverityBadge summary={summary({ highest_severity: null, misconfig_count: 3 })} onClick={() => {}} />);
+  expect(screen.getByRole('button', { name: /Findings/ })).toBeInTheDocument();
+});