- Updated `EnvelopeGenerator.Application.csproj` to include `Microsoft.Data.SqlClient` package.
- Refactored `CreateEnvelopeReceiverCommand` to inherit from `CreateEnvelopeCommand`.
- Enhanced `CreateEnvelopeSQL` with a SQL script for envelope creation.
- Introduced `CreateEnvelopeCommand` to encapsulate envelope creation data.
- Added `CreateEnvelopeCommandHandler` to process commands and interact with the database.
- Created `CreateEnvelopeResponse` class for handling responses from envelope creation.
Removed `DIExtensions.cs` and integrated its content into `DependencyExtensions.cs`, enhancing the dependency injection setup with repository and SQL executor registrations. Added a new `CreateEnvelopeSQL` class implementing the `ISQL<Envelope>` interface, currently with a placeholder implementation.