T07b: frontend feature pages — companies + contacts + settings + audit + dashboard + search

- 11 new feature pages (CompaniesList/Detail/Form, ContactsList/Detail/Form,
  SettingsProfile/Roles/Users, AuditLog, GlobalSearchResults)
- 3 page updates (Dashboard with StatCard+ActivityFeed, Settings with tree nav+Outlet,
  TopBar with SearchDropdown)
- 13 new routes in routes/index.tsx
- i18n updates (de.json + en.json) with companies/contacts/settings/audit/search keys
- 12 new test files + 2 existing test fixes (TopBar, AppShell)
- 7 shared components (DataGrid, Tabs, SearchDropdown, CsvImportDialog, StatCard,
  ActivityFeed, UnsavedChangesGuard)
- 16 new API hooks in hooks.ts
- Verification: 141 tests pass, build succeeds, tsc --noEmit clean

frontend/src/components/shared/StatCard.tsx

@@ -0,0 +1,36 @@
+import React from 'react';
+import clsx from 'clsx';
+import { Card } from '@/components/ui/Card';
+import { Badge, BadgeVariant } from '@/components/ui/Badge';
+
+export interface StatCardProps {
+  label: string;
+  value: string | number;
+  change?: string;
+  changeVariant?: BadgeVariant;
+  icon?: React.ReactNode;
+  testId?: string;
+}
+
+export function StatCard({ label, value, change, changeVariant = 'success', icon, testId }: StatCardProps) {
+  return (
+    <Card>
+      <div className="flex items-center justify-between" data-testid={testId}>
+        <div>
+          <p className="text-sm text-secondary-500">{label}</p>
+          <p className="text-2xl font-bold text-secondary-900 mt-1">{value}</p>
+          {change && (
+            <p className="text-xs mt-1">
+              <Badge variant={changeVariant} dot>{change}</Badge>
+            </p>
+          )}
+        </div>
+        {icon && (
+          <div className="w-12 h-12 rounded-lg bg-primary-50 flex items-center justify-center text-primary-600" aria-hidden="true">
+            {icon}
+          </div>
+        )}
+      </div>
+    </Card>
+  );
+}