[Feature] Implement sidebar view modes

As a user, I want to switch between date and folder views in the sidebar, so that I can organize conversations based on my current workflow needs.

As a user, I want multiple ways to view my threads in the sidebar, so that I can choose between chronological order or folder organization.

As a user, I want to toggle between date-based and folder-based sidebar views, so that I can navigate my conversations in the way that makes most sense for my task.