spec: map message payload schemas to CSA Appendix 2

Summary

The CSA NHP standard Appendix 2 defines logical fields for NHP message bodies such as KNK, ACK, AOP, ART, AOL, AAK, ACC, LOG, LAK, and ARD.

Current OpenNHP main uses implementation-specific JSON payloads and field names that do not obviously map 1:1 to Appendix 2. Examples:

• nhp/common/nhpmsg.go: AgentKnockMsg uses headerType, usrId, devId, orgId, aspId, resId, results, usrData.
• nhp/common/nhpmsg.go: ServerKnockAckMsg uses resHost, opnTime, aspToken, agentAddr, acTokens, preActions, redirectUrl.
• nhp/common/nhpmsg.go: ServerACOpsMsg uses srcAddrs and dstAddrs arrays rather than the standard's singular source/destination IP/port fields.
• NHP_LOG, NHP_LAK, and NHP_ARD payloads are not present in the current core message definitions.

Why This Matters

Even if message type numbers match, payload-level interoperability with a CSA-standard peer may fail unless the mapping is explicit. Integrators need to know which fields are compliant aliases, which are OpenNHP extensions, and which standard-required fields are missing.

Suggested Acceptance Criteria

• Build a message-by-message compliance matrix mapping CSA Appendix 2 fields to current OpenNHP JSON fields.
• Mark each difference as compliant alias, OpenNHP extension, missing standard field, or incompatible drift.
• Add JSON schema or golden-vector tests for standard message bodies.
• Implement missing required fields or compatibility adapters where strict standard compliance is required.
• Document any intentional OpenNHP extensions and version/feature negotiation behavior.