standalone: VoxelForgeCore link-safe next to Unreal -- internals in vfcore::detail, symbol check

- The copied generator, mesher and Compat stand-ins compile inside vfcore::detail.
- CheckCoreSymbols.ps1 (run by Build.ps1) fails on any unqualified Unreal-style symbol in the
  library: 16,255 on 557f6aa, 0 now. A UE 5.7 CoreMinimal.h + VoxelForgeCore.h smoke compile passes.
- Output identical: 11 hash rows at W1/W8, routes 5642/5642, look/passage/far audits pass,
  bad-shell control fails, six captures byte-identical.
Cost, measured by me interleaved (8 workers, cold, 4 runs each, first run excluded): 0.963 s vs
0.937 s for 557f6aa, ~27 ms in shape compilation; same math, so codegen/inlining. To be found.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Core/API.md

@@ -4,6 +4,11 @@ Public header: `Core/include/VoxelForgeCore/VoxelForgeCore.h` (C++20, standard l
 Build the static library and viewer with `Build.ps1 -Target All`, or only the library with
 `Build.ps1 -Target Core`.
 
+The public header uses only standard C++ types and can be included after Unreal's `CoreMinimal.h`.
+`Core/verification/UnrealHeaderCoexistence.cpp` is the compile smoke check against the installed
+Unreal 5.7 headers. Copied generator and compatibility declarations stay in the private
+`vfcore::detail` implementation and do not appear in this API.
+
 ## Units and ownership
 
 - `Vec3d` query positions and `Vec3i` voxel coordinates are in **voxels**.