feat(ui/agents): add NewSessionDialog

Modal collecting a repo URL, posts to createCloudSession, then surfaces
the new session to the parent for redirect into the three-pane view.

ui/litellm-dashboard/src/app/(dashboard)/agents/components/new-session-dialog.tsx

@@ -0,0 +1,73 @@
+"use client";
+
+/**
+ * NewSessionDialog — collects a repo URL and provisions a new session under
+ * an Agent. On success the parent navigates to the three-pane view, status
+ * pill = `provisioning`.
+ */
+import { useState } from "react";
+import { Modal, Form, Input, message } from "antd";
+import { createCloudSession } from "@/lib/cloud-agents-client";
+import type { CloudAgentSession } from "@/types/cloud-agents";
+
+interface NewSessionDialogProps {
+  open: boolean;
+  agentId: string;
+  accessToken: string | null;
+  onClose: () => void;
+  onCreated: (session: CloudAgentSession) => void;
+}
+
+export default function NewSessionDialog({ open, agentId, accessToken, onClose, onCreated }: NewSessionDialogProps) {
+  const [form] = Form.useForm<{ repo_url: string }>();
+  const [submitting, setSubmitting] = useState(false);
+
+  const handleOk = async () => {
+    try {
+      const values = await form.validateFields();
+      setSubmitting(true);
+      const session = await createCloudSession(accessToken, {
+        agent_id: agentId,
+        repo_url: values.repo_url,
+      });
+      message.success("Session provisioning…");
+      form.resetFields();
+      onCreated(session);
+    } catch (e) {
+      if (e instanceof Error) {
+        message.error(e.message);
+      }
+    } finally {
+      setSubmitting(false);
+    }
+  };
+
+  return (
+    <Modal
+      title="New session"
+      open={open}
+      onOk={handleOk}
+      onCancel={() => {
+        form.resetFields();
+        onClose();
+      }}
+      okText="Create session"
+      confirmLoading={submitting}
+      destroyOnClose
+      data-testid="new-session-dialog"
+    >
+      <Form form={form} layout="vertical" preserve={false}>
+        <Form.Item
+          name="repo_url"
+          label="Repository URL"
+          rules={[
+            { required: true, message: "Repository URL is required" },
+            { type: "url", message: "Must be a valid URL" },
+          ]}
+        >
+          <Input placeholder="https://github.com/owner/repo" data-testid="new-session-repo-url" />
+        </Form.Item>
+      </Form>
+    </Modal>
+  );
+}