…on logic

- Optimized `FileExplorerStateHolder` to offload heavy file scanning to `Dispatchers.IO` and perform UI state mapping on `Dispatchers.Default`.
- Implemented `combine` flow to efficiently merge raw directory data with selection state (`allowedDirectories`), preventing unnecessary file re-scans on selection toggles.
- Introduced `DirectoryEntry.isSelected` property to pre-calculate selection state in the ViewModel, removing expensive calculations from `FileExplorerBottomSheet` composition.
- Implemented "Smart View" (Flattened Mode) logic to strictly show folders with direct audio files and allow independent selection.
- Fixed logic in "Navigation Mode" (subtree selection) to correctly handle deselection of subtrees by stopping traversal when an excluded node is encountered.
- Optimized audio file counting to early-exit for performance while maintaining support for "99+" UI indicators.
- Ensured stable keys in `LazyColumn` for smoother scrolling and animations.

- Updated `SettingsViewModel.kt` to call the correct method `isDirectorySelected` from `FileExplorerStateHolder`, resolving an "Unresolved reference" error.
- Refactored `FileExplorerStateHolder` to optimize directory loading and selection logic, moving heavy tasks to background threads (`Dispatchers.IO`) and using `combine` for efficient state updates.
- Implemented `DirectoryEntry.isSelected` property to pre-calculate selection state, removing expensive calculations from UI composition.
- Implemented "Smart View" (Flattened Mode) logic to strictly show folders with direct audio files and allow independent selection.
- Fixed logic in "Navigation Mode" (subtree selection) to correctly handle deselection of subtrees by stopping traversal when an excluded node is encountered.
- Optimized audio file counting to early-exit for performance while maintaining support for "99+" UI indicators.
- Ensured stable keys in `LazyColumn` for smoother scrolling and animations.

- Resolved 'Unresolved reference' errors in `SettingsViewModel` and `SetupViewModel` by updating method calls to use `isDirectorySelected`.
- Updated `FileExplorerStateHolder` to expose `isDirectorySelected` correctly.
- Optimized file explorer performance by offloading scanning to `Dispatchers.IO` and using `combine` for state updates.
- Implemented robust 'Navigation Mode' (subtree selection) and 'Flattened Mode' (direct audio selection) logic.
- Added UI optimizations including `isSelected` pre-calculation and stable keys for `LazyColumn`.

Refactors `FileExplorerContent` to use a `Scaffold` for a more structured layout, moving the "Done" `ExtendedFloatingActionButton` to the `floatingActionButton` slot. The lazy column for file items now uses `weight(1f)` to fill available space.

The breadcrumb generation in `FileExplorerHeader` is moved to a background thread using `withContext(Dispatchers.IO)` to prevent UI freezes. The autoscroll behavior is also updated to use `animateScrollTo` for a smoother animation. Additionally, `AbsoluteSmoothCornerShape` has been replaced with the standard `RoundedCornerShape`.

…rmance-fix-4216163802957571506

Enhanced file explorer performance fix 4216163802957571506