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/DecalNet/FilterAdapterV1.h

@@ -0,0 +1,28 @@
+// FilterAdapterV1.h
+// Declaration of the filter adapter for V1 filters
+
+#ifndef __FILTERADAPTER_H
+#define __FILTERADAPTER_H
+
+#include <DecalNetImpl.h>
+
+class cFilterAdapterV1
+: public CComObjectRootEx< CComMultiThreadModel >,
+public ISoloNetworkFilterImpl< cFilterAdapterV1 >
+{
+   CComPtr<IUnknown> m_pV1;
+
+public:
+   HRESULT init ( REFCLSID clsid );
+
+BEGIN_COM_MAP(cFilterAdapterV1)
+   COM_INTERFACE_ENTRY(INetworkFilter2)
+   COM_INTERFACE_ENTRY_AGGREGATE_BLIND(m_pV1.p)
+END_COM_MAP()
+
+public:
+   // INetworkFilter2
+   STDMETHOD(DispatchServer)(IMessage2 *pMessage);
+};
+
+#endif