[Bug] Sidebar remains visible when entering fullscreen #315

Description
If fullscreen mode is entered while the sidebar is visible, the sidebar remains visible instead of being hidden. The sidebar should automatically hide when entering fullscreen. Once in fullscreen sidebar cannot be hidden.

Version

Fedora 44 COSMIC: 1.5.0^git20260728.23d5944

Steps to Reproduce

1. Open COSMIC Player.
2. Show the sidebar.
3. Enter fullscreen mode.

Expected Behavior
The sidebar is automatically hidden when entering fullscreen.