Add -DSLIC3R_CAD compile-time gate for the Design/CAD tab

Gate the entire parametric Design/CAD subsystem behind a single CMake
option so the fork can be built with or without it. With SLIC3R_CAD OFF
the build is behaviour-neutral against upstream OrcaSlicer; this is the
"parallel build" for upstream integration discussion.

Gated surface:
- option(SLIC3R_CAD) + add_definitions(-DSLIC3R_CAD)
- deps/OCCT/OCCT.cmake: BUILD_MODULE_ModelingAlgorithms=${SLIC3R_CAD}
  (OFF matches upstream OCCT exactly; ON adds only TKFillet + TKOffset)
- TKFillet/TKOffset link, add_subdirectory(slvs) + libslvs
- CAD kernel + GUI sources, GLGizmoPrimitive (needs GeometryEngine),
  CAD Catch2 tests
- 11 upstream C++ hook sites (GLCanvas3D, MainFrame, GLGizmosManager)
- TabPosition and gizmo EType enums switched to implicit numbering so
  OFF reproduces upstream indices exactly

Verified on behemoth both ways: OFF and ON link snapmaker-orca +
libslic3r_tests (exit 0); ON shows the Design tab and passes 8 [design]
+ 1 [Deviation] tests, OFF omits them and shows upstream's tab layout.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVzKmX6Y1aEteit1HTXG4Q

src/slic3r/GUI/GLCanvas3D.cpp

@@ -1,6 +1,8 @@
 #include "libslic3r/libslic3r.h"
 #include "GLCanvas3D.hpp"
+#ifdef SLIC3R_CAD
 #include "DesignSketchTool.hpp"   // SnapOrca Design: interactive 2D sketch tool
+#endif
 
 #include <igl/unproject.h>
 
@@ -2136,8 +2138,10 @@ void GLCanvas3D::render(bool only_init)
 
     // SnapOrca Design: interactive 2D sketch overlay, drawn over the scene but
     // beneath the UI overlays (toolbars, labels).
+#ifdef SLIC3R_CAD
     if (m_design_sketch_tool != nullptr && m_design_sketch_tool->has_display())
         m_design_sketch_tool->render(*this);
+#endif
 
     // draw overlays
     _render_overlays();
@@ -3297,6 +3301,7 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
     // SnapOrca Design: Delete/Backspace removes the selected sketch entities while a
     // sketch tool is active and the canvas has focus (dialog text fields are separate
     // wx controls, so this never eats their editing keys).
+#ifdef SLIC3R_CAD
     if (m_design_sketch_tool != nullptr && m_design_sketch_tool->is_active()
         && (keyCode == WXK_DELETE || keyCode == WXK_BACK)
         && !m_design_sketch_tool->selection().empty()) {
@@ -3305,9 +3310,11 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
         render();
         return;
     }
+#endif
 
     // Esc exits the active sketch tool (Onshape-like, layered: abort in-progress entity ->
     // drop to Select -> exit the session back to Feature mode).
+#ifdef SLIC3R_CAD
     if (m_design_sketch_tool != nullptr && m_design_sketch_tool->is_active()
         && keyCode == WXK_ESCAPE) {
         m_design_sketch_tool->request_exit();
@@ -3315,11 +3322,13 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
         render();
         return;
     }
+#endif
 
     // SnapOrca Design: Ctrl+Z / Ctrl+Shift+Z (and Ctrl+Y) undo/redo the Design feature
     // history. Scoped by m_design_sketch_tool — only the Design canvas owns one — so the
     // main 3D editor's undo/redo (the CanvasView3D-gated cases further below) is untouched.
     // Handled here, before the generic Ctrl block, so it takes precedence and early-returns.
+#ifdef SLIC3R_CAD
     if (m_design_sketch_tool != nullptr && (evt.GetModifiers() & ctrlMask) != 0) {
         const bool is_z = (keyCode == 'z' || keyCode == 'Z' || keyCode == WXK_CONTROL_Z);
         const bool is_y = (keyCode == 'y' || keyCode == 'Y' || keyCode == WXK_CONTROL_Y);
@@ -3331,10 +3340,12 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
             return;
         }
     }
+#endif
 
     // SnapOrca Design: F = Place on Face (Prepare's lay-flat), when the Design viewport is up
     // and a body face is selected. The tool forwards to DesignPanel::place_on_face; it returns
     // false (no face picked) so F falls through to the default handler below.
+#ifdef SLIC3R_CAD
     if (m_design_sketch_tool != nullptr && m_design_sketch_tool->has_display()
         && (keyCode == 'f' || keyCode == 'F') && (evt.GetModifiers() & ctrlMask) == 0) {
         if (m_design_sketch_tool->request_place_on_face()) {
@@ -3343,6 +3354,7 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
             return;
         }
     }
+#endif
 
     bool is_in_painting_mode = false;
     GLGizmoPainterBase *current_gizmo_painter = dynamic_cast<GLGizmoPainterBase *>(get_gizmos_manager().get_current());
@@ -3718,6 +3730,7 @@ void GLCanvas3D::on_key(wxKeyEvent& evt)
 {
     // SnapOrca Design: Delete/Backspace removes selected sketch entities. GTK delivers
     // these as KEY_DOWN rather than CHAR, so handle it here too.
+#ifdef SLIC3R_CAD
     if (evt.GetEventType() == wxEVT_KEY_DOWN
         && m_design_sketch_tool != nullptr && m_design_sketch_tool->is_active()
         && (evt.GetKeyCode() == WXK_DELETE || evt.GetKeyCode() == WXK_BACK)
@@ -3727,6 +3740,7 @@ void GLCanvas3D::on_key(wxKeyEvent& evt)
         render();
         return;
     }
+#endif
 
     static GLCanvas3D const * thiz = nullptr;
     static TranslationProcessor translationProcessor(nullptr, nullptr);
@@ -4263,6 +4277,7 @@ void GLCanvas3D::on_mouse(wxMouseEvent& evt)
     // can click to select. It runs after ImGui (so dialogs still work) but before
     // camera/toolbar/gizmo handling; on_mouse returns false for events it doesn't consume
     // (drag/orbit/wheel) so the camera keeps working over the display-only plate.
+#ifdef SLIC3R_CAD
     if (m_design_sketch_tool != nullptr && m_design_sketch_tool->has_display()) {
         if (evt.LeftDown() && m_canvas != nullptr)
             m_canvas->SetFocus();   // grab keyboard focus so Delete/keys reach this canvas
@@ -4272,6 +4287,7 @@ void GLCanvas3D::on_mouse(wxMouseEvent& evt)
             return;
         }
     }
+#endif
 
 #ifdef __WXMSW__
 	bool on_enter_workaround = false;