swarm-ui: a running-subagents menu in the full-screen terminal header

An N running subagents badge opens a list of the agent's subagents, each a
link to its terminal, so you can switch without going back to the agents page.
A subagent counts as running when it published a row in the last 15 minutes;
the quiet ones are listed below it, dimmed. The list under the preview and the
menu now share one fetch hook and one definition of running.

frontend/packages/swarm-ui/src/pages/agents/AgentTerminalPage.tsx

@@ -14,6 +14,7 @@ import type { RouteComponentProps } from "wouter-preact";
 import { Badge } from "@hive/shared/badge.js";
 import { AgentDetailPopover } from "../../agent/detail/AgentDetailPopover.js";
 import { AgentIcon } from "../../agent/AgentIcon.js";
+import { SubagentsMenu } from "../../agent/terminal/SubagentsMenu.js";
 import {
   AgentTermPreview,
   termPaths,
@@ -63,15 +64,18 @@ export function AgentTerminalPage({
         fullHeight
         showHeaderBadges
         leading={
-          <span ref={badgeRef}>
-            <Badge
-              icon={<AgentIcon name={name} small />}
-              value={name}
-              title={`${detailOpen ? "close" : "open"} ${name}'s details`}
-              expanded={detailOpen}
-              onClick={() => setDetailOpen((o) => !o)}
-            />
-          </span>
+          <>
+            <span ref={badgeRef}>
+              <Badge
+                icon={<AgentIcon name={name} small />}
+                value={name}
+                title={`${detailOpen ? "close" : "open"} ${name}'s details`}
+                expanded={detailOpen}
+                onClick={() => setDetailOpen((o) => !o)}
+              />
+            </span>
+            <SubagentsMenu agentName={name} current={subagent} />
+          </>
         }
       />
       <AgentDetailPopover