Updated `EnvelopeGenerator.Service.csproj` to target a single framework (`net4.6.2`) by replacing `<TargetFrameworks>` with `<TargetFramework>`.
Added `DefaultProfile.pubxml` to define a publish profile with settings for release configuration, platform, and file system-based publishing.
Introduced a new project `EnvelopeGenerator.Service` to the solution as a .NET Worker Service targeting the `net4.6.2` framework.
- Configured the project with nullable reference types, implicit usings, and `LangVersion` set to `latest`.
- Added a `Worker` class that logs periodic messages while running.
- Updated `Program.cs` to configure and run the Worker Service.
- Added `launchSettings.json` for development environment configuration.
- Added `appsettings.json` and `appsettings.Development.json` for logging configuration.
- Included the project in `EnvelopeGenerator.sln` with appropriate build configurations and hierarchy updates.
