VDE-002 (High): Fix submodule include path
- All target_include_directories: CMAKE_SOURCE_DIR → BUILD_INTERFACE
- Works as both standalone project and add_subdirectory()
VDE-006 (High): Break vde_mesh ↔ vde_brep circular dependency
- Move mesh-dependent code from brep to mesh module
- vde_brep no longer links vde_mesh
VDE-007 (Low): Add mirror() and mirror_about_plane() to transform.h
VDE-008 (Low): Add convenience accessors to StlTriangle (.x()/.y()/.z())
VDE-009 (Medium): Full Doxygen docs for C API + examples/capi/basic_usage.cpp
Pending: VDE-001/003/004/005/010 GCC compatibility (agent still running)