* fix(ui): remove fixed sessions button and mac titlebar coupling
Remove fixed sessions button from header on desktop Mac
Eliminate Mac titlebar spacer and drag-to-dock logic in sidebar
Update layout to rely on standard header/sidebar without mac-specific tweaks
* feat: improve mobile header with session toggle and back button
Add back button in mobile header to exit session switcher
Show Sessions label when session switcher is open in mobile header
Toggle between opening sessions and back navigation based on session state
Add file management API and UI components
Implement directory listing, search and CRUD operations in desktop backend
Expose new Files API on frontend to list, search, and modify files
Bohdan Triapitsyn