ifcviewer: split into shared library and two app executables

Turn src/ifcviewer into libIfcViewer.so holding the rendering engine +
geometry pipeline (ViewportWindow, GeometryStreamer, BvhAccel,
InstancedGeometry, SidecarCache, LodBuilder, AppSettings).  Move the
existing UI shell (MainWindow, SettingsWindow, main.cpp) into
src/ifcviewer-full as the IfcViewerFull executable.  Add a new
src/ifcviewer-minimal target with a MinimalWindow that hosts only the
viewport and reuses the sidecar fast-path for benchmark/debug runs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ifcviewer-full/CMakeLists.txt

@@ -0,0 +1,36 @@
+################################################################################
+#                                                                              #
+# This file is part of IfcOpenShell.                                           #
+#                                                                              #
+# IfcOpenShell is free software: you can redistribute it and/or modify         #
+# it under the terms of the Lesser GNU General Public License as published by  #
+# the Free Software Foundation, either version 3.0 of the License, or          #
+# (at your option) any later version.                                          #
+#                                                                              #
+# IfcOpenShell is distributed in the hope that it will be useful,              #
+# but WITHOUT ANY WARRANTY; without even the implied warranty of               #
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                 #
+# Lesser GNU General Public License for more details.                          #
+#                                                                              #
+# You should have received a copy of the Lesser GNU General Public License     #
+# along with this program. If not, see <http://www.gnu.org/licenses/>.         #
+#                                                                              #
+################################################################################
+
+message("Running CMakeLists.txt in /src/ifcviewer-full")
+
+file(GLOB IFCVIEWER_FULL_CPP_FILES ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp)
+file(GLOB IFCVIEWER_FULL_H_FILES ${CMAKE_CURRENT_SOURCE_DIR}/*.h)
+set(IFCVIEWER_FULL_FILES ${IFCVIEWER_FULL_CPP_FILES} ${IFCVIEWER_FULL_H_FILES})
+
+add_executable(IfcViewerFull ${IFCVIEWER_FULL_FILES})
+
+set_target_properties(IfcViewerFull PROPERTIES
+    AUTOMOC ON
+    WIN32_EXECUTABLE ON
+    MACOSX_BUNDLE ON
+)
+
+target_link_libraries(IfcViewerFull PRIVATE IfcViewer)
+
+install(TARGETS IfcViewerFull EXPORT ${IFCOPENSHELL_EXPORT_TARGETS})