feat(ui/agents): add AgentDetail for /agents/{aid}

Renders the agent identity, system prompt, and SessionList for this
agent. Settings hand-off link points at /settings/cloud-agents/ (Epic
G's territory) per coordination note in E1.md.

ui/litellm-dashboard/src/app/(dashboard)/agents/components/agent-detail.tsx

@@ -0,0 +1,123 @@
+"use client";
+
+/**
+ * AgentDetail — /agents/{agent_id} landing view.
+ *
+ * Renders the Agent's identity card, a settings hand-off link to
+ * /settings/cloud-agents/ (G's territory), and the SessionList for
+ * this agent. + New Session opens the create dialog.
+ */
+import { useEffect, useState } from "react";
+import Link from "next/link";
+import { useRouter } from "next/navigation";
+import { Card, Empty, Tag, Typography, Button, Space, message } from "antd";
+import dayjs from "dayjs";
+import SessionList from "@/app/(dashboard)/agents/components/session-list";
+import NewSessionDialog from "@/app/(dashboard)/agents/components/new-session-dialog";
+import { getCloudAgent, listCloudSessions } from "@/lib/cloud-agents-client";
+import type { CloudAgent, CloudAgentSession } from "@/types/cloud-agents";
+
+const { Title, Paragraph, Text } = Typography;
+
+interface AgentDetailProps {
+  agentId: string;
+  accessToken: string | null;
+}
+
+export default function AgentDetail({ agentId, accessToken }: AgentDetailProps) {
+  const router = useRouter();
+  const [agent, setAgent] = useState<CloudAgent | null>(null);
+  const [sessions, setSessions] = useState<CloudAgentSession[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [showNewSession, setShowNewSession] = useState(false);
+
+  useEffect(() => {
+    if (!accessToken) return;
+    let cancelled = false;
+    setLoading(true);
+    Promise.all([getCloudAgent(accessToken, agentId), listCloudSessions(accessToken, agentId)])
+      .then(([a, s]) => {
+        if (cancelled) return;
+        setAgent(a);
+        setSessions(s);
+      })
+      .catch((e: unknown) => {
+        if (!cancelled) {
+          const msg = e instanceof Error ? e.message : String(e);
+          message.error(`Failed to load agent: ${msg}`);
+        }
+      })
+      .finally(() => {
+        if (!cancelled) setLoading(false);
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [accessToken, agentId]);
+
+  return (
+    <div className="w-full p-6" data-testid="agent-detail">
+      <Space direction="vertical" size="large" className="w-full">
+        <div className="flex items-start justify-between gap-4">
+          <div className="min-w-0">
+            <Link href="/agents" className="!text-xs">
+              ← All agents
+            </Link>
+            <Title level={3} className="!mb-0 !mt-1">
+              {agent?.name ?? "Agent"}
+            </Title>
+            <Space size="small" className="mt-1">
+              {agent?.model && <Tag color="blue">{agent.model}</Tag>}
+              {agent?.last_activity_at && (
+                <Text type="secondary" className="!text-xs">
+                  Last activity {dayjs(agent.last_activity_at).fromNow?.() ?? agent.last_activity_at}
+                </Text>
+              )}
+            </Space>
+          </div>
+          <Space>
+            <Link href="/settings/cloud-agents/" data-testid="agent-settings-link">
+              <Button>Configure VM provider</Button>
+            </Link>
+            <Button type="primary" onClick={() => setShowNewSession(true)} data-testid="agent-detail-new-session-btn">
+              + New Session
+            </Button>
+          </Space>
+        </div>
+
+        {agent?.system_prompt && (
+          <Card size="small" data-testid="agent-system-prompt">
+            <Text strong>System prompt</Text>
+            <Paragraph className="!mb-0 !mt-1 whitespace-pre-wrap !text-sm">{agent.system_prompt}</Paragraph>
+          </Card>
+        )}
+
+        <Card title="Sessions" data-testid="agent-detail-sessions">
+          {sessions.length === 0 && !loading ? (
+            <Empty description="No sessions yet — start one to spin up a VM." />
+          ) : (
+            <div className="-mx-6 -my-2">
+              <SessionList
+                sessions={sessions}
+                loading={loading}
+                activeSessionId={null}
+                onNewSession={() => setShowNewSession(true)}
+              />
+            </div>
+          )}
+        </Card>
+      </Space>
+
+      <NewSessionDialog
+        open={showNewSession}
+        agentId={agentId}
+        accessToken={accessToken}
+        onClose={() => setShowNewSession(false)}
+        onCreated={(s) => {
+          setShowNewSession(false);
+          router.push(`/agents/${agentId}/sessions/${s.session_id}`);
+        }}
+      />
+    </div>
+  );
+}