🔄 Add Comprehensive Backup Management System

✨ New Features:
- Complete backup lifecycle management (create, list, download, delete, cleanup)
- Web-based backup interface with real-time status updates
- Individual backup deletion and bulk cleanup for old backups
- Docker-aware backup operations with volume persistence
- Automated backup scheduling and retention policies

📁 Added Files:
- backup.py - Core backup script for creating timestamped archives
- docker_backup.sh - Docker-compatible backup wrapper script
- app/templates/backup.html - Web interface for backup management
- BACKUP_SYSTEM.md - Comprehensive backup system documentation
- BACKUP_GUIDE.md - Quick reference guide for backup operations

🔧 Enhanced Files:
- Dockerfile - Added backup.py copy for container availability
- docker-compose.yml - Added backup volume mount for persistence
- app/routes/api.py - Added backup API endpoints (create, list, delete, cleanup)
- app/routes/main.py - Added backup management route
- app/templates/index.html - Added backup management navigation
- README.md - Updated with backup system overview and quick start

🎯 Key Improvements:
- Fixed backup creation errors in Docker environment
- Added Docker-aware path detection for container operations
- Implemented proper error handling and user confirmation dialogs
- Added real-time backup status updates via JavaScript
- Enhanced data persistence with volume mounting

💡 Use Cases:
- Data protection and disaster recovery
- Environment migration and cloning
- Development data management
- Automated maintenance workflows

app/templates/index.html

@@ -499,7 +499,10 @@
         <div class="header">
             <h1>🎯 QR Code Manager</h1>
             <p>Create, customize, and manage your QR codes with ease</p>
-            <div style="position: absolute; top: 20px; right: 20px;">
+            <div style="position: absolute; top: 20px; right: 20px; display: flex; gap: 10px;">
+                <a href="/backup" style="color: white; text-decoration: none; background: rgba(255,255,255,0.2); padding: 8px 15px; border-radius: 20px; font-size: 0.9em;">
+                    🛡️ Backup
+                </a>
                 <a href="/logout" style="color: white; text-decoration: none; background: rgba(255,255,255,0.2); padding: 8px 15px; border-radius: 20px; font-size: 0.9em;">
                     👤 Logout
                 </a>