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>

.gitignore

@@ -0,0 +1,24 @@
+# Build outputs
+bin/
+obj/
+Debug/
+Release/
+x86/
+x64/
+build/
+
+# IDE
+.vs/
+*.user
+*.suo
+*.sln.docstates
+
+# NuGet
+packages/
+
+# OS
+Thumbs.db
+.DS_Store
+
+# Native old source (reference only, not part of the build)
+# Keep Native/InjectModern/ and Native/LauncherHookModern/