Add one-click backup and restore functionality for system configuration and jobs

[Copilot]

This PR implements a comprehensive backup and restore feature that allows users to export and import their entire DDNS Updater configuration with a single click from the web interface.

Features Added

UI Components

• Added backup/restore button to the main navbar with cloud upload/download icon
• Created a dedicated backup modal with separate export and import sections
• Integrated seamlessly with existing Bootstrap styling and dark theme

Backend Implementation

• New Backup Service (pkg/backup/service.go): Handles complete data serialization and deserialization
• API Endpoints:
  • GET /api/backup/export - Downloads backup as timestamped JSON file
  • POST /api/backup/import - Uploads and restores from backup file
• Data Handling: Complete export of system configuration (YAML) and all DDNS jobs with proper encryption/decryption

Key Capabilities

• Complete Export: Backs up both system configuration and all DDNS jobs in a single JSON file
• Safe Import: Transactional restore process that replaces all existing data
• Security: Job parameters are properly encrypted in database, decrypted for backup, and re-encrypted on restore
• User Experience: Clear warnings and confirmations for destructive operations
• Versioning: Backup format includes version field for future compatibility

Example Backup Format

{
  "version": "1.0",
  "timestamp": "2025-08-01T06:45:23Z",
  "config": {
    "Interval": 600,
    "UseTOTP": false,
    "Port": 8080,
    "Resolver": ""
  },
  "jobs": [
    {
      "provider": "Custom",
      "params": "{\"URL\":\"http://example.com/update?ip=<ipv4>\",\"Check\":\"success\"}"
    }
  ]
}

Testing

The implementation has been thoroughly tested including:

• Backup export generates proper JSON with configuration and jobs
• Import successfully restores all data with transactional safety
• Job parameters correctly encrypted/decrypted throughout the process
• Full backup/restore cycle verified with sample DDNS jobs

This provides true "one-click" functionality as requested, enabling users to completely backup and restore their DDNS configuration through the web interface without any command-line interaction.

Fixes #380.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• api.ipify.org
  • Triggering command: ./main (dns block)
• api.ipy.ch
  • Triggering command: ./main (dns block)
• api.my-ip.io
  • Triggering command: ./main (dns block)
• httpbin.org
  • Triggering command: ./main (dns block)
• icanhazip.com
  • Triggering command: ./main (dns block)
• ident.me
  • Triggering command: ./main (dns block)
• ifconfig.me
  • Triggering command: ./main (dns block)
• nms.intellitrend.de
  • Triggering command: ./main (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.