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>

build.cmd

@@ -0,0 +1,51 @@
+@echo off
+REM Decal Open Source Build Script
+REM Builds all managed C# projects and the WiX installer.
+REM Native C++ projects (Inject.DLL, LauncherHook.DLL) must be built separately
+REM with Visual Studio 2022 or CMake (x86/Win32 target).
+
+echo ============================================
+echo  Decal Open Source Build
+echo ============================================
+echo.
+
+REM Step 1: Build managed solution
+echo [1/3] Building managed C# solution (25 projects)...
+dotnet build Managed\Decal.sln -c Release
+if errorlevel 1 (
+    echo ERROR: Managed build failed.
+    exit /b 1
+)
+echo Managed build succeeded.
+echo.
+
+REM Step 2: Build native C++ projects (requires Visual Studio 2022)
+echo [2/3] Native C++ projects...
+if exist "Native\build\Release\Inject.DLL" (
+    echo Native DLLs already built.
+) else (
+    echo NOTE: Native C++ projects must be built manually:
+    echo   cd Native
+    echo   cmake -G "Visual Studio 17 2022" -A Win32 -B build
+    echo   cmake --build build --config Release
+    echo.
+    echo Skipping native build for now.
+)
+echo.
+
+REM Step 3: Build installer (requires WiX Toolset v5)
+echo [3/3] Installer...
+if exist "%USERPROFILE%\.dotnet\tools\wix.exe" (
+    dotnet build Installer\Decal.Installer.wixproj -c Release ^
+        -p:BuildOutput=..\Managed\bin\Release ^
+        -p:NativeOutput=..\Native\build\Release
+) else (
+    echo NOTE: WiX Toolset not installed. Install with:
+    echo   dotnet tool install --global wix
+    echo Skipping installer build.
+)
+
+echo.
+echo ============================================
+echo  Build complete.
+echo ============================================