Add CultureService and localization support

Added a new `CultureService` to manage application culture and
localization. The service supports retrieving and setting the
application culture, storing it in `localStorage`, and initializing
it based on stored values, browser settings, or a default fallback.

Registered `CultureService` in the dependency injection container
and added localization support in `Program.cs` using
`builder.Services.AddLocalization()`.

EnvelopeGenerator.ReceiverUI/Program.cs

@@ -26,6 +26,7 @@ builder.Services.AddScoped<DocReceiverElementService>();
 builder.Services.AddScoped<SignatureCacheService>();
 builder.Services.AddSingleton<AppVersionService>();
 builder.Services.AddScoped<EnvelopeService>();
+builder.Services.AddScoped<CultureService>();
 
 // Localization services
 builder.Services.AddLocalization();