Add new properties to Signature class for database mapping

Added four new properties (`FullName`, `Position`, `Place`, and
`Ink`) to the `Signature` class. Each property is annotated with
the `[Column]` attribute to map to corresponding database columns
(`FULL_NAME`, `POSITION`, `PLACE`, and `INK`). The properties
support nullable values based on the `nullable` directive,
ensuring compatibility with nullable reference types. These
changes enhance the `Signature` class by enabling additional
data storage and retrieval.

EnvelopeGenerator.Domain/Entities/Signature.cs

@@ -126,5 +126,33 @@ namespace EnvelopeGenerator.Domain.Entities
         [NotMapped]
         public double Left => Math.Round(X, 5);
 #endif
+
+        [Column("FULL_NAME", TypeName = "nvarchar(100)")]
+        public string
+#if nullable
+        ?
+# endif
+            FullName { get; set; }
+
+        [Column("POSITION", TypeName = "nvarchar(100)")]
+        public string
+#if nullable
+        ?
+#endif
+            Position { get; set; }
+
+        [Column("PLACE", TypeName = "nvarchar(100)")]
+        public string
+#if nullable
+        ?
+#endif
+            Place { get; set; }
+
+        [Column("INK", TypeName = "varbinary(MAX)")]
+        public byte[]
+#if nullable
+        ?
+#endif
+            Ink { get; set; }
     }
 }