feat(Annotation): add Type property to Annotation entity and update CHANGED_WHO column type

- Added new required `Type` field with nvarchar(50) to `Annotation` entity.
- Updated `CHANGED_WHO` column type from nchar(100) to nvarchar(50).
- Corresponding database migration required.

EnvelopeGenerator.Domain/Entities/Annotation.cs

@@ -32,6 +32,10 @@ public class Annotation
     [Column("VALUE", TypeName = "nvarchar(max)")]
     public string Value { get; set; }
 
+    [Required]
+    [Column("TYPE", TypeName = "nvarchar(50)")]
+    public string Type { get; set; }
+
     [Required]
     [Column("ADDED_WHEN", TypeName = "datetime")]
     public DateTime AddedWhen { get; set; }
@@ -39,7 +43,7 @@ public class Annotation
     [Column("CHANGED_WHEN", TypeName = "datetime")]
     public DateTime? ChangedWhen { get; set; }
 
-    [Column("CHANGED_WHO", TypeName = "nchar(100)")]
+    [Column("CHANGED_WHO", TypeName = "nvarchar(100)")]
     [StringLength(100)]
     public string
 #if NET