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/Tools/IToolbox.cs

@@ -0,0 +1,30 @@
+using System.Reflection;
+using Microsoft.Extensions.AI;
+
+namespace Luna.Core.Tools;
+
+public interface IToolbox
+{
+    public string Name { get; }
+    
+    public sealed IEnumerable<AITool> GetTools()
+    {
+        var type = GetType();
+
+        List<(ToolAttribute Attribute, MethodInfo Method)> tools = [];
+        foreach (var method in type.GetMethods(BindingFlags.Public | BindingFlags.Instance))
+        {
+            var attribute = method.GetCustomAttribute<ToolAttribute>();
+            if (attribute is null) continue;
+            
+            tools.Add((attribute, method));
+        }
+        
+        return tools.Select(tool => AIFunctionFactory.Create(
+            tool.Method,
+            this,
+            $"{this.Name}/{tool.Attribute.Name}",
+            tool.Attribute.Description
+        ));
+    }
+}