Replace polling with websocket live sync

src/shared/contracts.ts

@@ -81,6 +81,29 @@ export interface DashboardSnapshot {
   };
 }
 
+export interface DashboardSnapshotPatch {
+  service?: DashboardSnapshot['service'];
+  traffic?: DashboardSnapshot['traffic'];
+  users?: DashboardSnapshot['users'];
+  attention?: DashboardSnapshot['attention'];
+  userRecords?: DashboardSnapshot['userRecords'];
+  system?: DashboardSnapshot['system'];
+}
+
+export type DashboardSyncMessage =
+  | {
+      type: 'snapshot.init';
+      snapshot: DashboardSnapshot;
+    }
+  | {
+      type: 'snapshot.patch';
+      patch: DashboardSnapshotPatch;
+    }
+  | {
+      type: 'session.expired';
+      error: string;
+    };
+
 export interface CreateUserInput {
   username: string;
   password: string;