Build only the OCCT and solver pieces the Design tab needs

SLIC3R_CAD=OFF now builds without SolveSpace or OCCT's ModelingAlgorithms
module, leaving the dependency set identical to upstream's, and the Design
tab's mate connector preference no longer appears in builds without the tab.
When the deps prefix and the project disagree about the option, the configure
fails naming the cause, rather than failing at link time or at first launch
on Windows. The Windows packaging step stages exactly the toolkits libslic3r
links.

deps/OCCT/OCCT.cmake

@@ -4,8 +4,9 @@ else()
     set(library_build_type "Static")
 endif()
 
-# The parametric Design/CAD tab is the only consumer of OCCT's ModelingAlgorithms
-# module (fillet/offset/loft). With it OFF the deps prefix matches upstream exactly.
+# SLIC3R_CAD (declared in deps/CMakeLists.txt) builds OCCT's ModelingAlgorithms module
+# (fillet/offset/loft), whose only consumer is the parametric Design/CAD tab. With it OFF
+# the deps prefix matches upstream exactly.
 #
 # With it ON the delta is THREE toolkits, not two: TKFillet (7.40 MiB archive, used via
 # BRepFilletAPI), TKOffset (5.38 MiB, used via BRepOffsetAPI) and TKFeat (4.42 MiB), which
@@ -17,9 +18,6 @@ endif()
 # shipped bytes. The Windows figure is a real DLL cost and has NOT been measured -- an
 # earlier "3.77 MiB, Windows only" note here covered only two of the three toolkits and is
 # not a number to quote. See docs/cad_dependency_weight.md.
-#
-# Must match the SLIC3R_CAD passed to the main project.
-option(SLIC3R_CAD "Build OCCT's ModelingAlgorithms module (required by the Design/CAD tab)" ON)
 
 if (IN_GIT_REPO)
     set(OCCT_DIRECTORY_FLAG --directory ${BINARY_DIR_REL}/dep_OCCT-prefix/src/dep_OCCT)