[FEATURE] Desktop sidebar: "last activity" filter / per-group limit should also work when grouped by folder

Problem
In the desktop app's Code tab, heavy users accumulate dozens of sessions per folder, and the sidebar grows without limit. The "last activity" filter (1/3/7/30 days) only appears when grouping by state. With group by folder, there is no way to show only recent sessions. The only workaround is manually archiving old sessions one by one.

Request (either would solve it)

1. Make the "last activity" filter available in every grouping mode, including folder grouping.
2. Add an option to show only the N most recent sessions per group (e.g. 5), with the rest behind "Show more".

Optional: an "auto-archive sessions inactive for N days" setting.

Why: Grouping by folder is the most useful view when working on several projects, but it becomes unusable once each folder has 20+ sessions.