[codex] add agent-platform core map

[fractional-pm]

Adds a first-pass agent-platform documentation overlay to AgentGraph.

What changed:

• Added an agent-platform/README.md entry point.
• Added a protocol registry covering identity, authorization, agent communication, and SurrealDB runtime protocols.
• Added a source organization inventory for didoneworld, openagx, and AGenNext repos.

Why:

• AgentGraph is the target repo for the platform map.
• The docs establish the boundary between external protocols and the ap:* governance layer.

Impact:

• Gives the repo a usable starting point for the agent-platform overlay.
• Makes the identity/access/protocol split explicit for follow-on development.

Validation:

• Reviewed against the current workspace notes and SurrealDB mapping docs.
• Published on a separate branch to avoid touching main directly.