fix: clear live agent status on cancel

Clear only active agent statuses when a session reaches idle, and keep the terminal cancelled/error run cleanup in place. Add regression coverage for idle cleanup after cancellation-like flows.

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

src/renderer/lib/sessionActivity.ts

@@ -46,6 +46,10 @@ export function applySessionEventActivity(
     if (event.status === 'running') {
       return removeSessionActivity(current, event.sessionId);
     }
+
+    if (event.status === 'idle') {
+      return clearActiveSessionActivity(current, event.sessionId);
+    }
   }
 
   if (