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>

Managed/Decal.DecalFilters/PrefilterImpl.cs

@@ -0,0 +1,31 @@
+using System.Runtime.InteropServices;
+using Decal.Interop.Filters;
+using Decal.Interop.Net;
+
+namespace Decal.DecalFilters
+{
+    [ComVisible(true)]
+    [Guid("443D4A68-5422-4E0C-9460-973F8FBDB190")]
+    [ClassInterface(ClassInterfaceType.None)]
+    [ComSourceInterfaces("Decal.Interop.Filters.IPrefilterEvents\0\0")]
+    [ProgId("DecalFilters.Prefilter")]
+    public class PrefilterImpl : IPrefilter, INetworkFilter2
+    {
+        public event IPrefilterEvents_EventEventHandler Event;
+
+        // IPrefilter is empty
+
+        public void Initialize(NetService pService) { }
+        public void Terminate() { }
+
+        public void DispatchServer(IMessage2 Message)
+        {
+            Event?.Invoke(Message.Type, (IMessage)Message);
+        }
+
+        public void DispatchClient(IMessage2 Message)
+        {
+            Event?.Invoke(Message.Type, (IMessage)Message);
+        }
+    }
+}