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/useNanobotStream.test.tsx

@@ -159,7 +159,8 @@ describe("useNanobotStream", () => {
 
   it("keeps streaming alive across stream_end and completes on turn_end", () => {
     const fake = fakeClient();
-    const { result } = renderHook(() => useNanobotStream("chat-s", EMPTY_MESSAGES), {
+    const onTurnEnd = vi.fn();
+    const { result } = renderHook(() => useNanobotStream("chat-s", EMPTY_MESSAGES, false, onTurnEnd), {
       wrapper: wrap(fake.client),
     });
 
@@ -211,5 +212,23 @@ describe("useNanobotStream", () => {
 
     expect(result.current.isStreaming).toBe(false);
     expect(result.current.messages.every((message) => !message.isStreaming)).toBe(true);
+    expect(onTurnEnd).toHaveBeenCalledTimes(1);
+  });
+
+  it("refreshes session metadata when the server reports a session update", () => {
+    const fake = fakeClient();
+    const onTurnEnd = vi.fn();
+    renderHook(() => useNanobotStream("chat-title", EMPTY_MESSAGES, false, onTurnEnd), {
+      wrapper: wrap(fake.client),
+    });
+
+    act(() => {
+      fake.emit("chat-title", {
+        event: "session_updated",
+        chat_id: "chat-title",
+      });
+    });
+
+    expect(onTurnEnd).toHaveBeenCalledTimes(1);
   });
 });