Initial commit: Complete open-source Decal rebuild

All 5 phases of the open-source Decal rebuild:

Phase 1: 14 decompiled .NET projects (Interop.*, Adapter, FileService, DecalUtil)
Phase 2: 10 native DLLs rewritten as C# COM servers with matching GUIDs
  - DecalDat, DHS, SpellFilter, DecalInput, DecalNet, DecalFilters
  - Decal.Core, DecalControls, DecalRender, D3DService
Phase 3: C++ shims for Inject.DLL (D3D9 hooking) and LauncherHook.DLL
Phase 4: DenAgent WinForms tray application
Phase 5: WiX installer and build script

25 C# projects building with 0 errors.
Native C++ projects require VS 2022 + Windows SDK (x86).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Native/DecalControls/Client.h

@@ -0,0 +1,50 @@
+// Client.h : Declaration of the cClient
+
+#ifndef __CLIENT_H_
+#define __CLIENT_H_
+
+#include "resource.h"       // main symbols
+
+#include "SinkImpl.h"
+
+/////////////////////////////////////////////////////////////////////////////
+// cClient
+class ATL_NO_VTABLE cClient : 
+	public CComObjectRootEx<CComMultiThreadModel>,
+	public CComCoClass<cClient, &CLSID_Client>,
+   public ILayerImpl,
+   public ILayerSchema,
+	public IClient
+{
+public:
+	cClient()
+	{
+	}
+
+   CComPtr< ILayerSite > m_pSite;
+
+   // TODO: Add support for background image and possibly
+   // scrolling
+
+DECLARE_REGISTRY_RESOURCEID(IDR_CLIENT)
+
+DECLARE_PROTECT_FINAL_CONSTRUCT()
+
+BEGIN_COM_MAP(cClient)
+   COM_INTERFACE_ENTRY(ILayerSchema)
+   COM_INTERFACE_ENTRY(ILayer)
+	COM_INTERFACE_ENTRY(IClient)
+END_COM_MAP()
+
+public:
+   // IClient Methods
+
+   // ILayer Methods
+   STDMETHOD(LayerCreate)(ILayerSite *pSite);
+   STDMETHOD(LayerDestroy)();
+
+   // ILayerSchema Methods
+   STDMETHOD(SchemaLoad)(IView *pView, IUnknown *pXMLSchema);
+};
+
+#endif //__CLIENT_H_