feat: add frontend action buttons, fix notification auth bug, add 53 Vitest tests

Bug fix:
- markNotificationRead was using raw fetch() without auth headers,
  bypassing the shared client's Authorization header. Moved to
  api/client.ts to use fetchJSON with proper auth.

New action buttons:
- CertificatesPage: "New Certificate" modal with form fields
- CertificateDetailPage: "Deploy" button with target selector modal,
  "Archive" button with confirmation
- IssuersPage: "Test Connection" and "Delete" per-row actions
- TargetsPage: "Delete" per-row action
- PoliciesPage: "Enable/Disable" toggle and "Delete" per-row actions

New API client functions:
- updateCertificate, archiveCertificate, registerAgent,
  createPolicy, updatePolicy, deletePolicy, getPolicyViolations,
  createIssuer, testIssuerConnection, deleteIssuer,
  createTarget, deleteTarget, markNotificationRead

Frontend tests (53 tests, 2 files):
- client.test.ts: 35 tests covering all API endpoints, auth headers,
  401 handling, error parsing, HTTP methods, request bodies
- utils.test.ts: 18 tests covering formatDate, formatDateTime,
  timeAgo, daysUntil, expiryColor

CI: Added "Run Frontend Tests" step to frontend-build job

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/pages/TargetsPage.tsx

@@ -1,5 +1,5 @@
-import { useQuery } from '@tanstack/react-query';
-import { getTargets } from '../api/client';
+import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
+import { getTargets, deleteTarget } from '../api/client';
 import PageHeader from '../components/PageHeader';
 import DataTable from '../components/DataTable';
 import type { Column } from '../components/DataTable';
@@ -17,11 +17,18 @@ const typeLabels: Record<string, string> = {
 };
 
 export default function TargetsPage() {
+  const queryClient = useQueryClient();
+
   const { data, isLoading, error, refetch } = useQuery({
     queryKey: ['targets'],
     queryFn: () => getTargets(),
   });
 
+  const deleteMutation = useMutation({
+    mutationFn: deleteTarget,
+    onSuccess: () => queryClient.invalidateQueries({ queryKey: ['targets'] }),
+  });
+
   const columns: Column<Target>[] = [
     {
       key: 'name',
@@ -60,6 +67,18 @@ export default function TargetsPage() {
       label: 'Created',
       render: (t) => <span className="text-xs text-slate-400">{formatDateTime(t.created_at)}</span>,
     },
+    {
+      key: 'actions',
+      label: '',
+      render: (t) => (
+        <button
+          onClick={(e) => { e.stopPropagation(); if (confirm(`Delete target ${t.name}?`)) deleteMutation.mutate(t.id); }}
+          className="text-xs text-red-400 hover:text-red-300 transition-colors"
+        >
+          Delete
+        </button>
+      ),
+    },
   ];
 
   return (