Yolop 0.18.4 release

Highlights

• ACP now advertises user-invocable skills to clients, and announces finished background work even when the wake turn stays silent.
• Action-guard gains a Muse-only idle-promise guard on the Jev classifier.
• MCP hardens workspace execution by blocking stdio process spawning and requiring explicit environment credential bindings.
• Observability and provider handling improve: Logfire forwards full LLM cost metadata and span duration, and Codex handles cross-provider reasoning.

See the GitHub release and the full release notes for every pull request in this version.