ci: wgpu sanity check on macOS

Lightweight workflow that compiles IfcViewerWgpu (the static lib) on
macOS arm64 + runs the wgpu state tests. Skips IfcViewerWgpuMinimal
because createSurface has no Metal path yet (task #32); the platform
surface blocks in WgpuViewportWindow.cpp are wrapped in
#if defined(Q_OS_LINUX) so the lib itself compiles cleanly on macOS.

Goal: catch portability regressions in the wgpu source on Apple
Silicon without paying for build_osx.yml's full IfcGeom + OCCT +
Python wheel pipeline. ~5 min vs hours.

Triggers on push/PR that touches src/ifcviewer-wgpu, the shared
headers it depends on, the top-level CMake, or this workflow itself.
Also workflow_dispatch for manual runs.

Hoists the Catch2 fetch in cmake/CMakeLists.txt out of the
BUILD_BONSAIVIEWER gate so the standalone wgpu config
(BUILD_BONSAIVIEWER=OFF + BUILD_BONSAIVIEWER_WGPU=ON +
BUILD_BONSAIVIEWER_TESTS=ON) can build tests without dragging the
whole bonsai/IfcGeom tree in. Default remains OFF, so default builds
stay offline-capable.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

cmake/CMakeLists.txt

@@ -681,24 +681,25 @@ if(BUILD_IFCGEOM)
 
     install(TARGETS ${IFCGEOM_SCHEMA_LIBRARIES} ${kernel_libraries} IfcGeom)
 endif(BUILD_IFCGEOM)
-if(BUILD_BONSAIVIEWER)
-    if(BUILD_BONSAIVIEWER_TESTS)
-        # Catch2 v3 — fetched on demand. Test option is OFF by default so the
-        # default build remains offline-capable.
-        include(FetchContent)
-        FetchContent_Declare(
-            Catch2
-            GIT_REPOSITORY https://github.com/catchorg/Catch2.git
-            GIT_TAG        v3.5.4
-            GIT_SHALLOW    TRUE
-        )
-        FetchContent_MakeAvailable(Catch2)
-        list(APPEND CMAKE_MODULE_PATH ${catch2_SOURCE_DIR}/extras)
-        include(CTest)
-        include(Catch)
-        enable_testing()
-    endif()
+# Catch2 fetch hoisted out of BUILD_BONSAIVIEWER so the standalone wgpu
+# build can also enable BUILD_BONSAIVIEWER_TESTS. Test option is OFF by
+# default so the default build remains offline-capable.
+if(BUILD_BONSAIVIEWER_TESTS)
+    include(FetchContent)
+    FetchContent_Declare(
+        Catch2
+        GIT_REPOSITORY https://github.com/catchorg/Catch2.git
+        GIT_TAG        v3.5.4
+        GIT_SHALLOW    TRUE
+    )
+    FetchContent_MakeAvailable(Catch2)
+    list(APPEND CMAKE_MODULE_PATH ${catch2_SOURCE_DIR}/extras)
+    include(CTest)
+    include(Catch)
+    enable_testing()
+endif()
 
+if(BUILD_BONSAIVIEWER)
     # Wgpu subprojects added first because IfcViewer's SceneLoader now
     # links against IfcViewerWgpu; the target must exist when IfcViewer's
     # CMakeLists runs.