Fall back for invalid Node interface port IDs

[shin4141]

Summary

• use the repository's existing 00-00-00-00-00-00 fallback when a Node interface port ID cannot be represented in the IS-04 six-octet lowercase-hyphen form
• leave valid port IDs unchanged
• keep host discovery and interface membership unchanged

Fixes #496.

Why

Tunnel and virtual interfaces may expose non-6-octet link-layer addresses. Since interfaces[].port_id requires the IS-04 six-octet lowercase-hyphen form, those values can make the Node resource schema-invalid. This change addresses the invalid port_id path reported in #496 by applying the existing null-address fallback at serialization.

Verification

• valid lowercase-hyphen port ID remains unchanged
• empty, 4/5/7-octet, malformed-hex, uppercase, and colon-separated inputs use the fallback
• focused tests: 3 test cases / 8 assertions
• affected NodeInterface tests: 6 test cases / 21 assertions
• full native suite: 186 test cases / 2597 assertions
• git diff --check

Scope

The regression uses controlled inputs and does not claim a Linux tunl0 end-to-end reproduction. This PR does not claim a maintainer preference for normalize over exclude, Sony adoption or acceptance, or cross-platform execution beyond the tested macOS arm64 / Apple clang 21 environment.