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/DTOs/TrackDto.cs

@@ -1,13 +1,21 @@
-namespace DeepDrftModels.DTOs;
+using Models.Models;
 
-public class TrackDto
+namespace DeepDrftModels.DTOs;
+
+// Inherits Id, CreatedAt, UpdatedAt from BaseModel (Cerebellum.BlazorBlocks.Models).
+// BlazorBlocks's Manager<> generic constraint requires `new()` on the model type, which
+// disqualifies `required` properties (the `new()` constraint and required members do not
+// compose). EntryKey/TrackName/Artist therefore drop `required` here — the TrackEntity
+// side remains required, and TrackConverter assigns every field on the round-trip so an
+// empty default is never observable in production code paths.
+public class TrackDto : BaseModel
 {
-    public long Id { get; set; }
-    public required string EntryKey { get; set; }
-    public required string TrackName { get; set; }
-    public required string Artist { get; set; }
+    public string EntryKey { get; set; } = string.Empty;
+    public string TrackName { get; set; } = string.Empty;
+    public string Artist { get; set; } = string.Empty;
     public string? Album { get; set; }
     public string? Genre { get; set; }
     public DateOnly? ReleaseDate { get; set; }
     public string? ImagePath { get; set; }
-}
+    public long? CreatedByUserId { get; set; }
+}