feat: retain live snapshots while revalidating (#139)

frontend/index.html

@@ -617,6 +617,9 @@ textarea { resize: vertical; min-height: 120px; }
     } else {
       setEventStreamStatus('Update failed · showing last activity');
     }
+    if (snapshot.freshness?.revalidating) {
+      setEventStreamStatus('Refreshing · showing recent snapshot');
+    }
   }