Add SenderAuthCookieHandler for cookie-based JWT auth

Added a custom DelegatingHandler, SenderAuthCookieHandler, to forward the browser's Cookie header to outgoing HttpClient requests in Blazor Server. Registered the handler as a transient service and integrated it into the named HttpClient pipeline for internal API calls. This enables Blazor Server components to make authenticated API calls using cookie-based JWT authentication (AuthScheme.Sender).

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Program.cs

@@ -69,6 +69,9 @@ try
     builder.Services.AddHttpContextAccessor();
 
     // Named HttpClient for internal API calls
+    // SenderAuthCookieHandler forwards the browser's Cookie header so that
+    // Blazor Server components can call cookie-authenticated endpoints (AuthScheme.Sender).
+    builder.Services.AddTransient<EnvelopeGenerator.Server.Handlers.SenderAuthCookieHandler>();
     builder.Services.AddHttpClient("EnvelopeGenerator.Server", (sp, client) =>
     {
         var httpContextAccessor = sp.GetRequiredService<IHttpContextAccessor>();
@@ -79,7 +82,8 @@ try
             // Set base address to current host for SSR scenarios
             client.BaseAddress = new Uri($"{request.Scheme}://{request.Host}");
         }
-    });
+    })
+    .AddHttpMessageHandler<EnvelopeGenerator.Server.Handlers.SenderAuthCookieHandler>();
 
     // CORS Policy
     var allowedOrigins = config.GetSection("AllowedOrigins").Get<string[]>() ??