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/Inject/PluginImpl.h

@@ -0,0 +1,60 @@
+// PluginImpl.h
+// Declaration of helper class for implementing plugins
+
+#ifndef __PLUGINIMPL_H
+#define __PLUGINIMPL_H
+
+template< class cImpl >
+class IPluginImpl
+: public IPlugin
+{
+public:
+   CComPtr< IPluginSite > m_pSite;
+
+   void onInitialize()
+   {
+   }
+
+   void onTerminate()
+   {
+   }
+
+   static LPCTSTR name()
+   {
+      // You must implement this function in the derived class
+      _ASSERTE( FALSE );
+
+      return _T( "ERROR: <unnamed plugin>" );
+   }
+
+   STDMETHOD(Initialize)( IPluginSite *pSite, long nID )
+   {
+      m_pSite = pSite;
+
+      static_cast< cImpl * >( this )->onInitialize();
+
+      return S_OK;
+   }
+
+   STDMETHOD(Terminate)()
+   {
+      static_cast< cImpl * >( this )->onTerminate();
+
+      m_pSite.Release();
+
+      return S_OK;
+   }
+
+   STDMETHOD(get_FriendlyName)( BSTR *pbstrName )
+   {
+      _ASSERTE( pbstrName != NULL );
+
+      *pbstrName = T2BSTR( cImpl::name() );
+      return S_OK;
+   }
+};
+
+// Included here for backward compatibility
+#include <EventsImpl.h>
+
+#endif // __PLUGINIMPL_H