Phase 0 Complete: Tasks 0.7-0.20

- 0.7: UI-Design-Richtlinien (docs/ui-design-guidelines.md, 535 lines)
- 0.8: Theme-Customization Backend (4 theme fields, migration 0023)
- 0.9: Theme-Customization Frontend (SettingsTheme.tsx, themeStore.ts, live preview)
- 0.10: RBAC-Audit (4 plugins secured, 53 routes with require_permission)
- 0.11: LiteLLM-Cleanup (llm_client.py migrated from httpx to litellm)
- 0.12: KI-Agent-Framework docs (plugin-development-guide.md, agent_capabilities field)
- 0.13: Heartbeat configurable (ProactiveSettings, migration 0024, frontend UI)
- 0.14: Unified Search Field-Level RBAC (resolve_permissions + filter_fields_by_permission)
- 0.15: Undo/History-System (EntityHistory model, service, routes, migration 0025, HistoryViewer)
- 0.16: Storage Backend (LocalStorage + S3Storage, DMS/attachments/mail updated)
- 0.17: Import/Export unified Contact fields (firstname, surname, email_1, phone_1)
- 0.18: .gitignore & Config-Cleanup (webui→frontend, python-jose removed, .env untracked)
- 0.19: Mail-Salt Security-Fix (per-account random salt, migration 0026)
- 0.20: AGPL replaced (PyMuPDF→pypdf, OnlyOffice→Collabora, LICENSE + THIRD_PARTY_LICENSES.md)

frontend/src/components/contacts/ContactDetail.tsx

@@ -8,6 +8,7 @@ import { Input } from '@/components/ui/Input';
 import { useToast } from '@/components/ui/Toast';
 
 import { Loader2 } from 'lucide-react';
+import { HistoryViewer } from '@/components/HistoryViewer';
 import {
   type UnifiedContact,
   type ContactPerson,
@@ -358,6 +359,13 @@ export function ContactDetail({ contact, loading, onEdit, onDeleted }: ContactDe
             </pre>
           </Section>
         )}
+
+        {/* History */}
+        {contact.id && (
+          <Section title={t('history.title', 'Änderungshistorie')}>
+            <HistoryViewer entityType="contact" entityId={contact.id} />
+          </Section>
+        )}
       </div>
 
       <ContactPersonModal