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/ActivityFeed.tsx

@@ -0,0 +1,41 @@
+import React from 'react';
+import { Card } from '@/components/ui/Card';
+import { Avatar } from '@/components/ui/Avatar';
+
+export interface ActivityItem {
+  id: string;
+  user: string;
+  action: string;
+  time: string;
+  avatarUrl?: string | null;
+}
+
+export interface ActivityFeedProps {
+  activities: ActivityItem[];
+  title?: string;
+  maxItems?: number;
+}
+
+export function ActivityFeed({ activities, title = 'Letzte Aktivitäten', maxItems = 10 }: ActivityFeedProps) {
+  const visible = activities.slice(0, maxItems);
+  return (
+    <Card title={title} data-testid="activity-feed">
+      {visible.length === 0 ? (
+        <p className="text-sm text-secondary-500 py-4 text-center">Keine Aktivitäten vorhanden.</p>
+      ) : (
+        <ul className="space-y-3" role="list">
+          {visible.map((activity) => (
+            <li key={activity.id} className="flex items-start gap-3 text-sm">
+              <Avatar name={activity.user} src={activity.avatarUrl} size="sm" />
+              <div className="flex-1 min-w-0">
+                <span className="font-medium text-secondary-900">{activity.user}</span>
+                <span className="text-secondary-600"> {activity.action}</span>
+                <span className="text-secondary-400 block mt-0.5">{activity.time}</span>
+              </div>
+            </li>
+          ))}
+        </ul>
+      )}
+    </Card>
+  );
+}