Add NetGuard — native macOS network scanner and security auditor

[Lyosis]

• I have read the Contribution Guidelines
• I confirm that I have read and understood the sections about "AI"-adjacent software
• Project URL: https://github.com/Lyosis/NetGuard
• Why should this project be added: NetGuard is a native macOS network scanner and security auditor built entirely in SwiftUI/Swift 6. It discovers all devices on the local network via ping sweep, port scan, mDNS/Bonjour, NetBIOS, and SSDP/UPnP; checks for open dangerous ports, expired SSL certificates, and default credentials; and runs a per-device risk score audit — all without sending any data outside the machine. No Electron, no telemetry, no subscription. Apple Silicon only.
• End all descriptions with a full stop/period ✓
• Entry is ordered alphabetically ✓ (between MIDAS and OS-X-Security-and-Privacy-Guide)
• Appropriate icon(s) added if applicable (OSS icon + Freeware icon) ✓