feat(proto): SurfaceState + SetState command + State event + SurfaceView.state

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/spacesh-proto/src/workspace.rs

@@ -2,6 +2,7 @@ use std::collections::HashMap;
 use serde::{Deserialize, Serialize};
 use crate::ids::{GroupId, SurfaceId, WorkspaceId};
 use crate::layout::LayoutNode;
+use crate::status::SurfaceState;
 
 /// Everything needed to (re)create a panel's process.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -50,6 +51,9 @@ pub struct SurfaceView {
     pub spec: SurfaceSpec,
     /// true = has a live actor/PTY; false = stopped (in tree, no process).
     pub running: bool,
+    /// Ephemeral agent-activity status (meaningful while running).
+    #[serde(default)]
+    pub state: SurfaceState,
 }
 
 /// Workspace view in `status` / `workspace_changed`: structure + per-surface state.