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/PluginAdapterV1.h

@@ -0,0 +1,48 @@
+// PluginAdapterV1.h : Declaration of the cPluginAdapterV1
+
+#ifndef __PLUGINADAPTERV1_H_
+#define __PLUGINADAPTERV1_H_
+
+#include "resource.h"       // main symbols
+#include <Decal.h>
+
+/////////////////////////////////////////////////////////////////////////////
+// cPluginAdapterV1
+class ATL_NO_VTABLE cPluginAdapterV1 : 
+	public CComObjectRootEx<CComSingleThreadModel>,
+	public CComCoClass<cPluginAdapterV1, &CLSID_PluginAdapterV1>,
+	public IPluginAdapterV1,
+   public IPlugin2,
+   public IDecalSurrogate
+{
+public:
+	cPluginAdapterV1()
+	{
+	}
+
+   CComPtr<IPluginSite2> m_pSite2;
+   CComPtr<IUnknown> m_pUnkPlugin;
+
+DECLARE_REGISTRY_RESOURCEID(IDR_PLUGINADAPTERV1)
+
+DECLARE_PROTECT_FINAL_CONSTRUCT()
+
+BEGIN_COM_MAP(cPluginAdapterV1)
+   COM_INTERFACE_ENTRY(IDecalSurrogate)
+   COM_INTERFACE_ENTRY(IPlugin2)
+	COM_INTERFACE_ENTRY(IPluginAdapterV1)
+   COM_INTERFACE_ENTRY_AGGREGATE_BLIND(m_pUnkPlugin.p)
+END_COM_MAP()
+
+// IPluginAdapterV1
+public:
+
+   // IPlugin2
+   STDMETHOD(Initialize)(IPluginSite2 *pSite2);
+   STDMETHOD(Terminate)();
+
+   // IDecalSurrogate
+   STDMETHOD(CreateInstance)(IDecalEnum *pEnum, REFIID riid, LPVOID *ppvItf);
+};
+
+#endif //__PLUGINADAPTERV1_H_