- Created include/vde/curves/continuity_types.h with both enum definitions
- Removed duplicate Continuity enum from curve_tools.h and surface_extension.h
- Removed duplicate ContinuityLevel enum from surface_editing.h and surface_continuity.h
- All four headers now include continuity_types.h
- Eliminates redefinition errors when multiple headers are included together
- Build: 100% success (all targets, 0 errors)