Fix custom folder selection in disk tools

[Dezoff-max]

Summary

• fix the Custom Folder source in Disk Analysis and Duplicate Finder
• open the native folder panel after the current SwiftUI picker update
• keep the previous source when the panel is cancelled
• activate Custom Folder only after an actual folder selection
• prevent duplicate picker requests while the panel is open

Verification

• Debug Xcode build passed
• signed Debug launch verification passed
• both Russian Custom Folder segments opened the native panel
• cancel preserved Downloads in Duplicate Finder
• selecting Documents activated Custom Folder and displayed the exact path in both sections
• no scan started automatically
• all 40 SwiftPM tests passed