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/EchoFilter.rgs

@@ -0,0 +1,39 @@
+HKCR
+{
+	DecalFilters.EchoFilter.1 = s 'DecalFilters EchoFilter'
+	{
+		CLSID = s '{8C2FA400-315D-41DE-B063-D6EF04F12E1F}'
+	}
+	DecalFilters.EchoFilter = s 'DecalFilters EchoFilter'
+	{
+		CLSID = s '{8C2FA400-315D-41DE-B063-D6EF04F12E1F}'
+		CurVer = s 'DecalFilters.EchoFilter.1'
+	}
+	NoRemove CLSID
+	{
+		ForceRemove {8C2FA400-315D-41DE-B063-D6EF04F12E1F} = s 'DecalFilters EchoFilter'
+		{
+			ProgID = s 'DecalFilters.EchoFilter.1'
+			VersionIndependentProgID = s 'DecalFilters.EchoFilter'
+			InprocServer32 = s '%MODULE%'
+			{
+				val ThreadingModel = s 'Both'
+			}
+			'TypeLib' = s '{3559E08B-827E-4DFE-9D33-3567246849CC}'
+		}
+	}
+}
+
+HKLM
+{
+   NoRemove SOFTWARE
+   {
+      NoRemove Decal
+      {
+         NoRemove NetworkFilters
+         {
+            val {8C2FA400-315D-41DE-B063-D6EF04F12E1F} = d '1'
+         }
+      }
+   }
+}