Keep library navigable during refresh - show loading indicator in title instead

[mmcdole]

When refreshing a library (via keybind), the current content is cleared and replaced with a loading indicator, making it impossible to navigate while the refresh is in progress.

Current behavior:

• Refresh triggered → m.Loading = true → UI shows "Loading..."
• Library content inaccessible until refresh completes

Desired behavior:

• Keep existing library content visible and navigable during refresh
• Load updated library content into a separate location in the background
• Replace library contents all at once when refresh completes
• Move loading indicator to the library title or status area (e.g., spinner next to library name)

This allows continuing to browse/play media while a background refresh is happening.