Support Muse Code as a detected agent

[mjdouglas]

I would like to add built-in Muse Code support to Herdr.

I am a member of the official Muse Code team (Meta's terminal coding agent, muse CLI) and I use it inside Herdr day-to-day. Today it runs as unknown — no sidebar state, no notifications, no herdr agent wait.

Proposed support:

• screen-manifest state detection (idle / working / blocked), the same model as Claude Code and Codex
• herdr integration install muse for session identity, following the session-identity-only pattern (like hermes/agy): a Herdr-owned hook reports the native session id, state stays with screen detection
• session restore via muse resume <id> after a Herdr restart

I already implemented this locally and verified it against the live Muse UI:

• idle, working, and blocked (request-user-input) all detect through full prompt → work → question → answer cycles
• the startup workspace-trust dialog reports blocked instead of falling back to idle
• state returns cleanly after answering, and resume picks up the same session

This follows the same model Herdr already uses for the other supported agents, and I can help with screen evidence or UI questions from the Muse side.

Related: #2390.