Add 6 new test cases covering previously untested branches:
- Empty host returns error
- Whitespace-only host returns error
- Unknown node type keeps host without port
- Docker node type keeps host without port
- IPv4 address gets default port
- IPv4 with custom port preserved
Coverage improved from 92.6% to 96.3%.
Cover API validation functions that were previously untested:
- validateIPAddress: IPv4/IPv6 validation with edge cases
- validatePort: Port range validation (1-65535)
- defaultPortForNodeType: Proxmox node type to default port mapping