feat(webui): polish chat layout and titles

Align the WebUI sidebar and chat chrome with the updated design, and generate WebUI session titles asynchronously without blocking turns.

Co-authored-by: Cursor <cursoragent@cursor.com>

webui/src/tests/api.test.ts

@@ -1,6 +1,6 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
 
-import { deleteSession, fetchSessionMessages, updateSettings } from "@/lib/api";
+import { deleteSession, fetchSessionMessages, listSessions, updateSettings } from "@/lib/api";
 
 describe("webui API helpers", () => {
   beforeEach(() => {
@@ -48,4 +48,28 @@ describe("webui API helpers", () => {
       }),
     );
   });
+
+  it("maps generated session titles from the sessions list", async () => {
+    vi.mocked(fetch).mockResolvedValueOnce({
+      ok: true,
+      json: async () => ({
+        sessions: [
+          {
+            key: "websocket:chat-1",
+            created_at: "2026-05-01T10:00:00",
+            updated_at: "2026-05-01T10:01:00",
+            title: "优化 WebUI 标题",
+          },
+        ],
+      }),
+    } as Response);
+
+    await expect(listSessions("tok")).resolves.toMatchObject([
+      {
+        key: "websocket:chat-1",
+        title: "优化 WebUI 标题",
+        preview: "",
+      },
+    ]);
+  });
 });