swarm-ui: the agents page is one column of cards that open in place

The roster loses its second column and its table view. Selecting a card opens
its details under it as four folded sections: overview, settings, accounts and
the terminal. The status, message and wanted rows, which the card header
already shows, are gone from the details. The terminal page's details dialog
keeps the flat list.

frontend/packages/swarm-ui/src/agent/detail/AgentDetail.css

@@ -17,3 +17,11 @@
   align-items: center;
   gap: 0.75em;
 }
+
+/* The folded sections of an opened card sit one under another, each with the
+   shared disclosure look; the fields keep the grid above. */
+.ui-agent-detail-sections {
+  display: flex;
+  flex-direction: column;
+  gap: 0.75em;
+}