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.

DeepDrftContent.Data/Constants/VaultConstants.cs

@@ -0,0 +1,12 @@
+namespace DeepDrftContent.Data.Constants;
+
+/// <summary>
+/// Constants for FileDatabase vault names
+/// </summary>
+public static class VaultConstants
+{
+    /// <summary>
+    /// Vault name for storing audio tracks
+    /// </summary>
+    public const string Tracks = "tracks";
+}