chat-messages: add timeline module with builder, grouping, items, and rendering.

surfsense_web/features/chat-messages/timeline/items/reasoning-item.tsx

@@ -0,0 +1,15 @@
+import type { FC } from "react";
+import type { ReasoningItem as ReasoningItemModel } from "../types";
+import { ItemHeader } from "./item-header";
+
+/**
+ * Renders a ``kind: "reasoning"`` row — pure agent narration with no
+ * tool component beneath it. Just the shared header.
+ *
+ * Native ``<think>`` blocks (model-level reasoning) are NOT rendered
+ * here — they live in the body via assistant-ui's ``Reasoning``
+ * component.
+ */
+export const ReasoningItem: FC<{ item: ReasoningItemModel }> = ({ item }) => (
+	<ItemHeader title={item.title} status={item.status} items={item.items} itemKey={item.id} />
+);