Add Luna.Core server with SignalR hub, session management, and tool system

Implement the core application server as an ASP.NET web host with:
- SignalR ChatHub for real-time client communication
- Session management with token estimation for context windowing
- Extensible tool system with attribute-based tool discovery
- Chat stream update builder for streaming AI responses
- App configuration with appsettings for development and production

Luna.Core/Services/Extensions/ServiceCollectionExtensions.cs

@@ -0,0 +1,21 @@
+using Luna.Configuration.Extensions;
+using Luna.Core.Abstractions;
+using Luna.Core.Session;
+
+namespace Luna.Core.Services.Extensions;
+
+public static class ServiceCollectionExtensions
+{
+    extension(IServiceCollection services)
+    {
+        public IServiceCollection AddSessionManager()
+        {
+            services.AddTransient<IChatStreamUpdateBuilder, ChatStreamUpdateBuilder>();
+            
+            services.AddSessionOptions();
+            services.AddSingleton<ISessionManager, SessionManager>();
+            
+            return services;
+        }
+    }
+}