fix(app): never auto-focus subagents on workspace open

pickAttentionAgent now skips agents with a parentAgentId. The
workspace auto-focus path was opening subagents as tabs when they
needed attention, breaking the rule that subagents only become tabs
when the user explicitly clicks them.

packages/app/src/utils/agent-attention.ts

@@ -38,6 +38,10 @@ export function pickAttentionAgent(agents: Agent[]): string | null {
       continue;
     }
 
+    if (agent.parentAgentId) {
+      continue;
+    }
+
     const priority = getAttentionPriority(agent.attentionReason);
     if (priority === null) {
       continue;