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/ChoiceDropDown.h

@@ -0,0 +1,49 @@
+// ChoiceDropDown.h : Declaration of the cChoiceDropDown
+
+#ifndef __CHOICEDROPDOWN_H_
+#define __CHOICEDROPDOWN_H_
+
+#include "resource.h"       // main symbols
+
+#include <SinkImpl.h>
+
+class cChoice;
+
+/////////////////////////////////////////////////////////////////////////////
+// cChoiceDropDown
+class ATL_NO_VTABLE cChoiceDropDown : 
+	public CComObjectRootEx<CComMultiThreadModel>,
+   public ILayerImpl< cChoiceDropDown >,
+   public ILayerRenderImpl,
+   public ILayerPopup,
+   public cNoEventsImpl,
+	public IChoiceDropDown
+{
+public:
+	cChoiceDropDown()
+      : m_pChoice( NULL )
+	{
+	}
+
+   cChoice *m_pChoice;
+
+DECLARE_PROTECT_FINAL_CONSTRUCT()
+
+BEGIN_COM_MAP(cChoiceDropDown)
+   COM_INTERFACE_ENTRY(ILayerRender)
+   COM_INTERFACE_ENTRY(ILayerPopup)
+   COM_INTERFACE_ENTRY(ILayer)
+	COM_INTERFACE_ENTRY(IChoiceDropDown)
+END_COM_MAP()
+
+// IChoiceDropDown
+public:
+
+   // ILayerRender Methods
+   STDMETHOD(Reformat)();
+
+   // ILayerPopup Methods
+   STDMETHOD(PopupCancel)(MouseState *pMS, VARIANT_BOOL *pbContinue);
+};
+
+#endif //__CHOICEDROPDOWN_H_