Export Chat feature no longer working

## Problem

The "Export chat" button at the top right of the Q Developer chat window no longer works. Clicking on the button brings up the save dialog to save the chat export in markdown or HTML format, but after clicking Save no file is created.

I can confirm this was working as of about 2 weeks ago (just prior to the Agent mode update) but I'm not sure which update introduced this issue.

## Steps to reproduce the issue

1. Open a workspace with the Amazon Q Developer extension active and navigate to the Q chat window.
2. Click on the Export Chat icon in the top right of the chat panel.
3. Enter a desired filename, choose between markdown or HTML export, and click Save.
4. No export file is actually created.

## Expected behavior

An export of the current chat history would be saved with the designated filename and format.

## System details (run `Amazon Q: About`)

- OS: Windows_NT x64 10.0.19045
- Visual Studio Code extension host: 1.99.3
- Amazon Q: 1.66.0
- node: 20.18.3
- electron: 34.3.2

Start in the Amazon Q chat window by reproducing the Export chat flow on the reported VS Code, Amazon Q, Node, and Electron versions. Done means saving the current chat creates a file with the chosen filename in both Markdown and HTML formats.

Written by the indexing model from the issue text.