Add authority proxy end-to-end decision tests

[ocularminds]

Context

The current authority image smoke test proves that an unreachable control plane fails closed. It does not exercise successful control-plane responses or every enforcement outcome.

Scope

Run the authority proxy against a deterministic mock control plane and verify its HTTP and MCP adapter behavior.

Acceptance criteria

• Tests cover allow, block, review/escalate, malformed response, timeout, and unreachable-control-plane cases.
• Non-allow outcomes never produce an empty MCP interceptor body.
• Response status, reason codes, and dossier metadata are asserted without logging credentials.
• Tests run in the Build & Test matrix on pull requests.
• A regression fixture documents the expected protocol boundary.