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/DecalFilters/EchoFilter2.cpp

@@ -0,0 +1,22 @@
+// EchoFilter.cpp : Implementation of cEchoFilter
+#include "stdafx.h"
+#include "DecalFilters.h"
+#include "EchoFilter2.h"
+
+/////////////////////////////////////////////////////////////////////////////
+// cEchoFilter
+
+
+STDMETHODIMP cEchoFilter2::DispatchServer(IMessage2 *pMsg)
+{
+   Fire_EchoServer( pMsg );
+
+	return S_OK;
+}
+
+STDMETHODIMP cEchoFilter2::DispatchClient(IMessage2 *pMsg)
+{
+   Fire_EchoClient( pMsg );
+
+	return S_OK;
+}