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.DecalDat/DatStreamImpl.cs

@@ -0,0 +1,70 @@
+using System;
+using System.Runtime.InteropServices;
+using Decal.Interop.Dat;
+
+namespace Decal.DecalDat
+{
+    [ComVisible(true)]
+    [Guid("9F7F6CD9-D164-418D-8CB5-3B9ACD70BEAF")]
+    [ClassInterface(ClassInterfaceType.None)]
+    [ProgId("DecalDat.DatStream")]
+    public class DatStreamImpl : IDatStream
+    {
+        private DatFileEntry _file;
+
+        internal void Load(DatFileEntry file)
+        {
+            _file = file;
+        }
+
+        public int Size => _file?.Size ?? 0;
+
+        public int Tell => _file?.Tell ?? 0;
+
+        public void Skip(int Bytes)
+        {
+            _file?.Skip(Bytes);
+        }
+
+        public void Restart()
+        {
+            _file?.Reset();
+        }
+
+        public void ReadBinary(int Bytes, ref byte Buffer)
+        {
+            if (_file == null) return;
+
+            var buf = new byte[Bytes];
+            _file.Read(buf, 0, Bytes);
+
+            // Copy to unmanaged buffer starting at ref Buffer
+            Marshal.Copy(buf, 0, GetBufferPtr(ref Buffer), Bytes);
+        }
+
+        public string Read(int Bytes)
+        {
+            if (_file == null) return string.Empty;
+
+            var buf = new byte[Bytes];
+            int read = _file.Read(buf, 0, Bytes);
+
+            // Return as binary BSTR (same as SysAllocStringByteLen in C++)
+            unsafe
+            {
+                fixed (byte* p = buf)
+                {
+                    return Marshal.PtrToStringAnsi(new IntPtr(p), read);
+                }
+            }
+        }
+
+        private static unsafe IntPtr GetBufferPtr(ref byte buffer)
+        {
+            fixed (byte* p = &buffer)
+            {
+                return new IntPtr(p);
+            }
+        }
+    }
+}