feat: show per-agent activity statuses

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/shared/domain/event.ts

@@ -16,6 +16,7 @@ export interface SessionEventRecord {
   authorName?: string;
   contentDelta?: string;
   activityType?: SessionActivityType;
+  agentId?: string;
   agentName?: string;
   toolName?: string;
   error?: string;