Add EnvelopeGenerator.ServiceHost ASP.NET Core Web API project

Created a new EnvelopeGenerator.ServiceHost project targeting .NET 8.0. Set up minimal API host with controllers, Swagger/OpenAPI support, and development configuration files. Updated solution to include the new project with appropriate build settings.

EnvelopeGenerator.ServiceHost/Program.cs

@@ -0,0 +1,28 @@
+using EnvelopeGenerator.ServiceHost;
+
+var builder = WebApplication.CreateBuilder(args);
+
+// Add services to the container.
+
+builder.Services.AddControllers();
+
+// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
+builder.Services.AddEndpointsApiExplorer();
+builder.Services.AddSwaggerGen();
+
+var app = builder.Build();
+
+// Configure the HTTP request pipeline.
+if (app.Environment.IsDevelopment())
+{
+    app.UseSwagger();
+    app.UseSwaggerUI();
+}
+
+app.UseHttpsRedirection();
+
+app.UseAuthorization();
+
+app.MapControllers();
+
+app.Run();