Set default culture to German (de-DE)

Configured the application's default thread culture to "de-DE" using the `CultureInfo` class. This ensures consistent localization and formatting for dates, numbers, and other culture-dependent elements throughout the application.

FoodsharingSiegen.Server/Program.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using Blazorise;
 using Blazorise.Icons.Material;
 using Blazorise.Material;
@@ -34,6 +35,8 @@ builder.Services
     .AddMaterialProviders()
     .AddMaterialIcons();
 
+CultureInfo.DefaultThreadCurrentCulture = new("de-DE");
+
 var app = builder.Build();
 app.ApplyMigrations();