feat: add in-memory database support via appsettings UseInMemoryDb flag

- Introduced conditional EF Core configuration to support InMemoryDatabase for testing or lightweight runs.
- Added `UseInMemoryDb` config flag read from appsettings.
- Retained SQL Server as the default when the flag is false.
- Added missing Quartz namespace import.

EnvelopeGenerator.Finalizer/Program.cs

@@ -6,6 +6,7 @@ using EnvelopeGenerator.Infrastructure;
 using MediatR;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Options;
+using Quartz;
 using Serilog;
 
 // Load Serilog from appsettings.json
@@ -58,8 +59,9 @@ try
             opt.AddDbContext((provider, options) =>
             {
                 var logger = provider.GetRequiredService<ILogger<EGDbContext>>();
-                options.UseSqlServer(connStr)
-                        .LogTo(log => logger.LogInformation("{log}", log), LogLevel.Trace)
+                var useInMemoryDb = config.GetValue<bool>("UseInMemoryDb");
+                var dbCtxOpt = useInMemoryDb ? options.UseInMemoryDatabase("EGInMemoryDb") : options.UseSqlServer(connStr);
+                dbCtxOpt.LogTo(log => logger.LogInformation("{log}", log), LogLevel.Trace)
                         .EnableSensitiveDataLogging()
                         .EnableDetailedErrors();
             });