Migrate legacy VB.NET service to modern C# Worker

Migrated the legacy VB.NET Windows Service to a modern C# Worker Service targeting .NET Framework 4.6.2. Key changes include:

- Added `Microsoft.Extensions.Hosting.WindowsServices`, `NLog`, and `Quartz` for logging and scheduling.
- Introduced `LogConfigFactory` to bridge `ServiceConfig` and `LogConfig` for Quartz jobs.
- Rewrote `Worker` to handle the full service lifecycle, including database connection, temp file management, and scheduler initialization.
- Implemented `SchedulerFinishEnvelope` and `SchedulerEnvelopeTaskApi` for Quartz job scheduling.
- Created `TempFiles` for service-level temp file management.
- Configured `NLog` for file and console logging.
- Updated `appsettings.json` for connection strings and service-specific configuration.
- Replaced legacy `ProjectInstaller` with `AddWindowsService()` for SCM integration.

EnvelopeGenerator.Service/Program.cs

@@ -1,7 +1,41 @@
 using EnvelopeGenerator.Service;
+using EnvelopeGenerator.Service.Schedulers;
+using Microsoft.Extensions.Options;
+using NLog.Extensions.Logging;
 
 var builder = Host.CreateApplicationBuilder(args);
+
+// NLog
+builder.Logging.ClearProviders();
+builder.Logging.AddNLog("nlog.config");
+
+// Configuration
+builder.Services.Configure<ServiceConfig>(
+    builder.Configuration.GetSection("ServiceConfig"));
+
+// Resolve connection string once for singleton registrations
+var connectionString = builder.Configuration.GetConnectionString("Default")
+    ?? throw new InvalidOperationException("ConnectionStrings:Default is not configured.");
+
+// Services
+builder.Services.AddSingleton<TempFiles>();
+
+builder.Services.AddSingleton<SchedulerFinishEnvelope>(sp => new SchedulerFinishEnvelope(
+    sp.GetRequiredService<ILogger<SchedulerFinishEnvelope>>(),
+    sp.GetRequiredService<IOptions<ServiceConfig>>(),
+    connectionString));
+
+builder.Services.AddSingleton<SchedulerEnvelopeTaskApi>(sp => new SchedulerEnvelopeTaskApi(
+    sp.GetRequiredService<ILogger<SchedulerEnvelopeTaskApi>>(),
+    sp.GetRequiredService<IOptions<ServiceConfig>>(),
+    connectionString));
+
 builder.Services.AddHostedService<Worker>();
 
+// Windows Service (SCM) support — replaces legacy ProjectInstaller/installutil
+builder.Services.AddWindowsService(options =>
+    options.ServiceName = "EnvelopeGenerator.Service");
+
 var host = builder.Build();
 host.Run();
+