Group the rail's open bot with its sessions

The active row and its session previews now share one highlighted card,
with a hairline thread from the bot's icon down to the last session.

src/layouts/bots/(partials)/rail-bot-entry.tsx

@@ -1,6 +1,8 @@
 import type { BotWithLastMessage } from "@/src/types";
 import BotRow from "./bot-row";
+import RailBotCard from "./rail-bot-card";
 import RailBotSessions from "./rail-bot-sessions";
+import Divider from "@moduletrace/twui/layout/Divider";
 
 type Props = {
     bot: BotWithLastMessage;
@@ -12,11 +14,24 @@ type Props = {
 /**
  * A worker in the rail, and its sessions while it is the open conversation.
  */
-export default function RailBotEntry({ bot, href, selected, workspace_id }: Props) {
+export default function RailBotEntry({
+    bot,
+    href,
+    selected,
+    workspace_id,
+}: Props) {
     return (
-        <>
+        <RailBotCard selected={selected}>
             <BotRow bot={bot} href={href} selected={selected} />
-            {selected ? <RailBotSessions key={bot.id} bot={bot} workspace_id={workspace_id} /> : null}
-        </>
+            {selected ? (
+                <>
+                    <RailBotSessions
+                        key={bot.id}
+                        bot={bot}
+                        workspace_id={workspace_id}
+                    />
+                </>
+            ) : null}
+        </RailBotCard>
     );
 }