feat(data): rename *.Services projects, lift TrackEntity onto BlazorBlocks data layer, regenerate initial Postgres migration

DeepDrftWeb.Services → DeepDrftData; DeepDrftContent.Services → DeepDrftContent.Data.
TrackEntity:BaseEntity, TrackRepository:Repository<>, TrackManager:Manager<>+ITrackService.
Drops DeepDrftModels PagingParameters/PagedResult in favour of Models.Common.* from BlazorBlocks.
InitialCreate migration captures full schema including is_deleted index.

DeepDrftModels/Entities/TrackEntity.cs

@@ -1,8 +1,12 @@
-namespace DeepDrftModels.Entities;
+using Models.Entities;
 
-public class TrackEntity
+namespace DeepDrftModels.Entities;
+
+// Inherits Id, CreatedAt, UpdatedAt, IsDeleted from BaseEntity (Cerebellum.BlazorBlocks.Models).
+// BaseEntity ships the audit columns but does not declare IEntity itself, so subclasses
+// declare it explicitly to satisfy the generic constraints on Repository<>/Manager<>/etc.
+public class TrackEntity : BaseEntity, IEntity
 {
-    public long Id { get; set; }
     public required string EntryKey { get; set; }
     public required string TrackName { get; set; }
     public required string Artist { get; set; }
@@ -11,4 +15,4 @@ public class TrackEntity
     public DateOnly? ReleaseDate { get; set; }
     public string? ImagePath { get; set; }
     public long? CreatedByUserId { get; set; }
-}
+}