Improve file operations, layout memory, and drive status.

Add a sequential file-operations queue with pause, reorder, and optional auto-clear; persist window size and tree width; show free space; and clear leftover indexing status.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/Explorer.Domain/Abstractions/IIndexStore.cs

@@ -68,6 +68,7 @@ public interface IScanJobStore
     Task<long> InsertAsync(ScanJob job, CancellationToken cancellationToken = default);
     Task UpdateAsync(ScanJob job, CancellationToken cancellationToken = default);
     Task InterruptRunningAsync(CancellationToken cancellationToken = default);
+    Task<bool> HasActiveAsync(long sourceId, CancellationToken cancellationToken = default);
     Task AddErrorAsync(ScanError error, CancellationToken cancellationToken = default);
     Task<ScanJob?> GetAsync(long id, CancellationToken cancellationToken = default);
     Task<IReadOnlyList<ScanJob>> GetRecentAsync(int take, CancellationToken cancellationToken = default);