Allow NVRs on Management VLAN in security audit

[tvancott42]

Summary

• NVRs (UNVR, UNVR-Pro, Cloud Key) are now accepted on Management or Security VLANs - previously all Protect devices were classified as cameras and flagged Critical if not on the Security VLAN, causing false positives for dual-homed NVRs
• NVR-specific issue title and recommendation - when an NVR is on the wrong VLAN, the audit shows "NVR on Wrong VLAN" and recommends both Management and Security VLANs as valid targets
• Regular cameras unchanged - cameras (including Protect cameras) are still required to be on the Security VLAN only

Closes #268

Test plan

• 14 new unit tests covering NVR placement, detection metadata, message format, and regression guards
• All 4,977 tests pass with 0 warnings
• Run security audit on NAS - verify existing camera issues unchanged
• Run security audit on Mac - verify existing camera issues unchanged
• User with UNVR on Management VLAN confirms false positive is resolved