GUID name instead of paste.png

When pasting a picture on Window client, the file name chosen is always paste.png. It would be better to have a .png name to be able to have a unique name for easier downloading.

The issue concerns image pasting in the Windows client, where pasted files are named paste.png. Start by locating the Windows paste-image entry point and its filename handling, then verify that generated names are unique and retain the .png extension. No file or test is named in the issue, so inspect existing paste or download tests if available.

Written by the indexing model from the issue text.