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/Luna.Core.csproj

@@ -0,0 +1,28 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <AllowMissingPrunePackageData>true</AllowMissingPrunePackageData>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="10.0.4"/>
+    <PackageReference Include="Microsoft.Extensions.AI" Version="10.4.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Luna.Agents.Abstractions\Luna.Agents.Abstractions.csproj" />
+    <ProjectReference Include="..\Luna.Agents\Luna.Agents.csproj" />
+    <ProjectReference Include="..\Luna.Channels.Abstractions\Luna.Channels.Abstractions.csproj" />
+    <ProjectReference Include="..\Luna.Channels\Luna.Channels.csproj" />
+    <ProjectReference Include="..\Luna.Configuration\Luna.Configuration.csproj" />
+    <ProjectReference Include="..\Luna.Core.Abstractions\Luna.Core.Abstractions.csproj" />
+    <ProjectReference Include="..\Luna.Memory\Luna.Memory.csproj" />
+    <ProjectReference Include="..\Luna.Providers.Abstractions\Luna.Providers.Abstractions.csproj" />
+    <ProjectReference Include="..\Luna.Providers\Luna.Providers.csproj" />
+    <ProjectReference Include="..\Luna.Shared\Luna.Shared.csproj" />
+  </ItemGroup>
+
+</Project>