Add option to sort sidebar sessions by recency instead of alphabetical/folder grouping

The session sidebar now groups sessions by project folder, with folders listed alphabetically. Previously sessions were listed by recency (most-recently-used first), which made it much faster to jump back into active work.

The current alphabetical/folder grouping breaks that workflow — with many project folders, finding a recently active session now requires scanning through folders in alphabetical order instead of just looking at the top of the list.

Request: Add a setting or toggle to sort/list sessions by most-recently-used, either as the default or as an option alongside the folder-grouped view.