Refactor SQL handling in EnvelopeGenerator application

- Added `System.Data` using directive in `EnvelopeCreateReadSQL.cs`.
- Updated SQL command strings to use parameter placeholders.
- Corrected method name from `CreateParmas` to `CreateParams` and added output parameter `@OutUid`.
- Made similar updates in `EnvelopeReceiverAddReadSQL.cs`.
- Introduced `ParamsExtensions` class with `ToSqlParam` method for converting .NET objects to SQL-safe parameter strings.

EnvelopeGenerator.Application/SQL/ParamsExtensions.cs

@@ -0,0 +1,28 @@
+namespace EnvelopeGenerator.Application.SQL;
+
+/// <summary>
+/// Extension method for converting objects to SQL parameter strings.
+/// </summary>
+public static class ParamsExtensions
+{
+    /// <summary>
+    /// Converts a .NET object to its corresponding SQL-safe parameter string.
+    /// </summary>
+    /// <param name="obj">The object to convert.</param>
+    /// <returns>A string representing the SQL parameter.</returns>
+    public static string ToSqlParam(this object? obj)
+    {
+        if (obj is null)
+            return "NULL";
+        else if (obj is string strVal)
+            return $"'{strVal}'";
+        else if (obj is bool boolVal)
+            return boolVal ? "1" : "0";
+        else if (obj is double doubleVal)
+            return $"'{doubleVal}'";
+        else if (obj is int intVal)
+            return intVal.ToString();
+        else
+            throw new NotSupportedException($"Type '{obj.GetType().FullName}' is not supported for SQL parameter conversion.");
+    }
+}