Progress updates not showing during scan and UI performance degradation with large file counts

[jotarios]

Description

During volume scanning, progress updates are not showing in the UI after the initial "Starting scan of [Volume]..." message. Additionally, when scanning large hard drives or volumes with many files, the UI becomes unresponsive.

Steps to Reproduce

1. Start scanning a large external volume with many audio files
2. Observe the progress message in the sidebar
3. Notice that it only shows "Starting scan of [Volume]..." and doesn't update
4. Try to interact with the UI during the scan
5. Notice the UI is frozen/unresponsive

Expected Behavior

• Progress updates should show frequently during scanning:
  • Current folder being scanned
  • Number of files found so far
  • Real-time feedback as the scan progresses
• UI should remain responsive during long-running scans

Current Behavior

• Only shows "Starting scan of [Volume]..."
• No further progress updates are visible
• UI freezes during scan on large volumes
• User cannot interact with the application while scanning

Technical Details

• Progress callback is called every 50 files and for each directory
• Progress updates are wrapped in Task { @MainActor in ... }
• Scan runs in Task.detached background thread
• Batch size: 2000 files
• Related to issue UI freezes during volume scanning #2 (UI freezing during volume scanning)

Files Affected

• prism/Scanner/FileScanner.swift
• prism/ViewModels/SearchViewModel.swift
• prism/Views/SidebarView.swift

Observations

The issue appears to be worse with:

• Large hard drives (1TB+)
• High file counts (10,000+ files)
• Deep directory structures