swarm-ui, hive dashboard, agent page: one profile menu with the signed-in user, avatar and authelia links

The swarm UI's user menu moves to @hive/shared and takes the whoami URL and
authelia's URL as props; the swarm UI keeps a thin wrapper, and the hive
dashboard and the per-agent page mount the same component. The dashboard's
nginx vhost proxies /api/whoami to authelia (the agent page is served from
the same vhost), and hive-c0re's state carries authelia_public_url, set from
services.hyperhive.swarm.authelia.url. The agent page shows the menu only
behind the gateway.

frontend/packages/agent/src/components/AgentUserMenu.tsx

@@ -0,0 +1,44 @@
+// <AgentUserMenu> — the profile menu (`@hive/shared/user-menu.js`) in this
+// page's header. Only behind the gateway: the page is then on the dashboard's
+// own origin, where the session cookie is valid and nginx proxies
+// `/api/whoami` to authelia. Opened directly on the agent's own port there is
+// no sign-in to show, so the page has no menu.
+//
+// Authelia's URL, for the settings and sign-out links, comes from the
+// dashboard's `/api/state` (`authelia_public_url`), the one place hive-c0re
+// states it.
+import { useEffect, useState } from "preact/hooks";
+import { UserMenu } from "@hive/shared/user-menu.js";
+import "@hive/shared/user-menu.css";
+import { isBehindGateway } from "../lib/dashboardBase.js";
+
+export function AgentUserMenu({ dashboardBase }: { dashboardBase: string }) {
+  const behind = isBehindGateway();
+  const [autheliaUrl, setAutheliaUrl] = useState<string | null>(null);
+
+  useEffect(() => {
+    if (!behind) return;
+    let cancelled = false;
+    fetch(`${dashboardBase}api/state`)
+      .then((r) =>
+        r.ok ? r.json() : Promise.reject(new Error(`http ${r.status}`)),
+      )
+      .then((state: { authelia_public_url?: string | null }) => {
+        if (!cancelled) setAutheliaUrl(state.authelia_public_url ?? null);
+      })
+      .catch(() => {
+        /* cosmetic only: the menu then shows the name without the links */
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [behind, dashboardBase]);
+
+  if (!behind) return null;
+  return (
+    <UserMenu
+      whoamiUrl={`${dashboardBase}api/whoami`}
+      autheliaUrl={autheliaUrl}
+    />
+  );
+}