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/Program.cs

@@ -0,0 +1,50 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Luna.Agents.Extensions;
+using Luna.Channels.Extensions;
+using Luna.Configuration.Extensions;
+using Luna.Core.Abstractions;
+using Luna.Core.Hubs;
+using Luna.Core.Services.Extensions;
+using Luna.Core.Tools.Extensions;
+using Luna.Memory.Extensions;
+using Luna.Providers.Extensions;
+
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Configuration
+    .AddLunaConfiguration();
+
+builder.Services
+    .AddOpenApi()
+    .AddProviders()
+    .AddAgents()
+    .AddTools()
+    .AddMemoryStore()
+    .AddSessionManager()
+    .AddChannels();
+
+builder.Services.AddSignalR()
+    .AddJsonProtocol(options =>
+    {
+        options.PayloadSerializerOptions.Converters.Add(
+            new JsonStringEnumConverter(JsonNamingPolicy.CamelCase));
+    });
+builder.Services.AddTransient<IChatHubContext, ChatHubContext>();
+    
+var app = builder.Build();
+
+// Configure the HTTP request pipeline.
+if (app.Environment.IsDevelopment())
+{
+    app.MapOpenApi();
+}
+
+app.MapHub<ChatHub>("/chat");
+app.Run();
+
+// Expose Program type for WebApplicationFactory in integration tests
+namespace Luna.Core
+{
+    public partial class Program { }
+}