feat: implement comprehensive backup and restore system with S3 support

- Add S3/MinIO storage adapter with multipart upload support
- Implement database backup service for SQLite and PostgreSQL
- Create backup manifest generator for tracking backup contents
- Enhance backup service with S3 integration and incremental backups
- Add restore service with safety measures and rollback capability
- Create comprehensive test suite for all backup functionality
- Add admin API endpoints for backup/restore management
- Implement frontend UI with dashboard, configuration, and restore wizard
- Add roadmap section to README with implemented backup feature

This implementation provides:
- Multiple backup destinations (local, rsync, S3/MinIO)
- Intelligent change detection to minimize backup frequency
- Full database backups with compression
- Manifest-based restore with integrity validation
- Pre-restore safety backups with rollback
- Comprehensive error handling and monitoring
- User-friendly admin interface

🤖 Generated with Claude Code

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

frontend/src/App.tsx

@@ -21,7 +21,8 @@ import {
   AnalyticsPage,
   BrandingPage,
   SettingsPage,
-  CMSPage
+  CMSPage,
+  BackupManagement
 } from './pages/admin';
 import { CMSPageEnhanced } from './pages/admin/CMSPageEnhanced';
 import { AdminLayout, AdminAuthWrapper } from './components/admin';
@@ -124,6 +125,7 @@ function App() {
                       <Route path="analytics" element={<AnalyticsPage />} />
                       <Route path="branding" element={<BrandingPage />} />
                       <Route path="settings" element={<SettingsPage />} />
+                      <Route path="backup" element={<BackupManagement />} />
                       <Route path="cms" element={<CMSPageEnhanced />} />
                       <Route index element={<Navigate to="/admin/dashboard" replace />} />
                     </Route>