fix: revert grace period, increase poll interval to 500ms to prevent doubles without adding jitter

apps/monitor/src/main.rs

@@ -41,6 +41,6 @@ async fn main() -> Result<()> {
             Ok(n) => { if n > 0 { info!("Spawned {n} checks"); } },
             Err(e) => error!("Check cycle failed: {e}"),
         }
-        sleep(Duration::from_millis(50)).await;
+        sleep(Duration::from_millis(500)).await;
     }
 }