I just had a quick look and I think you can use the _http_requests and _users views to get this information. The http_user_agent field contains the standard user agent strings you get when looking at HTTP logs so you could determine the browser or if they logged in on a mobile device. They also display Tableau 7000.xxxx for desktop users connecting to server views and the tabcmd requests too.
The currentsheet field is blank for the Tableau Desktop rows, but the http_request_url contains the workbook path so you could use this instead.
Lastly though, I'm pretty sure these logs are truncated weekly or something like that. I have heard of others who do daily dumps of the postgres data into their main data warehouse for historical, so you may have to look at doing that going forward.