Update culture handling and adjust middleware order

Changed GetCulture to return current UI culture if cookie is missing, ensuring a non-null result. Reordered middleware in Program.cs to run ExceptionHandlingMiddleware after CultureMiddleware.

EnvelopeGenerator.Web/Program.cs

@@ -187,8 +187,8 @@ try
 
     var app = builder.Build();
 
-    app.UseMiddleware<ExceptionHandlingMiddleware>();
     app.UseMiddleware<CultureMiddleware>();
+    app.UseMiddleware<ExceptionHandlingMiddleware>();
 
     // Configure the HTTP request pipeline.
     if (!app.Environment.IsDevelopment())