Add CLI client application with SignalR connectivity

Implement standalone CLI client that connects to Luna.Core via SignalR
for interactive chat sessions. Includes ChatClientService for managing
the hub connection and streaming responses, with a hosted service
architecture using Microsoft.Extensions.Hosting.

Luna.Clients.Cli/Program.cs

@@ -0,0 +1,9 @@
+using Luna.Cli;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+var builder = Host.CreateApplicationBuilder(args);
+builder.Logging.ClearProviders();
+builder.Services.AddHostedService<ChatClientService>();
+await builder.Build().RunAsync();