feat: Health command — version, pid, started_at (proto + daemon)

crates/spacesh-proto/src/message.rs

@@ -122,6 +122,7 @@ pub enum Cmd {
         limit: Option<u32>,
     },
     MarkRead { target: MarkReadTarget },
+    Health,
     Status,
     Shutdown,
 }
@@ -321,6 +322,15 @@ mod tests {
         assert_eq!(back, evt);
     }
 
+    #[test]
+    fn health_cmd_round_trips() {
+        let env = Envelope::Req { id: 1, cmd: Cmd::Health };
+        let j = serde_json::to_string(&env).unwrap();
+        assert!(j.contains(r#""cmd":"health""#));
+        let back: Envelope = serde_json::from_str(&j).unwrap();
+        assert_eq!(back, env);
+    }
+
     #[test]
     fn event_log_cmd_no_limit_round_trips() {
         let env = Envelope::Req { id: 9, cmd: Cmd::EventLog { limit: None } };