Add cloudshell-fog and AgentPlane adapter scaffolds

[mdheller]

Summary

Adds dependency-free adapter scaffolds for cloudshell-fog and AgentPlane.

This PR implements the first tested execution/shell boundary for issue #7 without claiming live service integration yet.

It adds:

• cloudshell_fog.py with session request/attach adapter primitives.
• agentplane.py with validation, placement, run, replay, and artifact-reference primitives.
• In-memory test backends for both planes.
• Tests proving shell request/attach and AgentPlane run/replay fail closed without Policy Fabric decision metadata.
• Tests proving admitted paths preserve policy, agent, workroom, topic, Matrix, session, executor, audit, and artifact metadata.

Boundary decisions

• AgentTerm does not open local privileged shells.
• cloudshell-fog remains the authority for OIDC, placement, TTL, PTY attach, and audit semantics.
• AgentTerm does not execute bundles.
• AgentPlane remains the authority for validation, placement, run, replay, and evidence artifacts.
• Shell attach and AgentPlane run/replay require Policy Fabric decision references.
• When non-human agents initiate these flows, Agent Registry IDs are preserved in metadata.

Validation

Expected CI:

ruff check .
pytest

Part of #7.