Fix 9 design majors: ITrackService interface, IsDescending, ArrayPool base, CliUtils, sort sentinel cleanup, content controller via TrackService, Skip property

DeepDrftWeb.Services/Repositories/TrackRepository.cs

@@ -26,11 +26,18 @@ public class TrackRepository
 
     public async Task<PagedResult<TrackEntity>> GetPage(PagingParameters<TrackEntity> pageParameters)
     {
+        // Two separate queries with no transaction: count and page can be momentarily inconsistent
+        // under concurrent writes. Acceptable — SQLite concurrency is low and the UI is read-only.
+        // If filtering is added, the count query must be updated to apply the same filter.
         var count = await _db.Tracks.CountAsync();
-        
-        var page = await _db.Tracks
-            .OrderBy(pageParameters.OrderBy ?? (t => t.Id))
-            .Skip((pageParameters.Page - 1) * pageParameters.PageSize)
+
+        var orderBy = pageParameters.OrderBy ?? (t => t.Id);
+        var ordered = pageParameters.IsDescending
+            ? _db.Tracks.OrderByDescending(orderBy)
+            : _db.Tracks.OrderBy(orderBy);
+
+        var page = await ordered
+            .Skip(pageParameters.Skip)
             .Take(pageParameters.PageSize)
             .ToListAsync();