Route bonsai through wgpu; delete the GL backend

Bonsai now drives the wgpu viewport for both sidecar and direct-IFC
loads. The GL viewer and its supporting state classes are gone.

SceneLoader rewire:
- Takes WgpuViewportWindow* instead of ViewportWindow*.
- Sidecar path reads metadata only (readSidecarMetadataOnly) and hands
  the StreamingSidecar off to the new applyCachedModel. Field accesses
  inside applySidecarData go through .meta.
- Direct-IFC path uses the wgpu A-path (upload{Mesh,Instance}Chunk +
  finalizeModel). The applyLodExtension call is dropped — wgpu has no
  live LOD1 splice; LOD1 still lands in the on-disk sidecar for the
  next open.

Bonsai migration:
- ViewportWindow → WgpuViewportWindow across MainWindow, Measurement,
  SessionState, and every modules/*/{Commands,Panel,View}.{h,cpp} —
  116 sites total. Same s/OverlayRenderer::/WgpuOverlayRenderer::/
  rename, 12 sites.
- Includes flipped from ../ifcviewer/ViewportWindow.h to
  ../ifcviewer-wgpu/WgpuViewportWindow.h. OverlayRenderer.h include
  dropped (transitively reached via the viewport header).
- BonsaiViewer links IfcViewerWgpu in addition to IfcViewer for the
  duration of the migration; the GL-side IfcViewer also publicly links
  IfcViewerWgpu so SceneLoader can resolve WgpuViewportWindow.

GL backend deletion:
- src/ifcviewer/ViewportWindow.{cpp,h}, BvhAccel.*, OverlayRenderer.*,
  Selection.*, Visibility.* all gone.
- src/ifcviewer-minimal/ removed entirely (MinimalWindow drove the GL
  viewport).
- src/ifcviewer/tests: test_bvh_accel, test_selection, test_visibility
  removed. The first has no replacement (wgpu doesn't use a per-instance
  BVH); the latter two are ported separately. test_lod_builder,
  test_sidecar_cache, test_instanced_geometry, test_federation remain
  (backend-agnostic).
- IfcViewer's CMakeLists drops OpenGL, Qt::OpenGL, Qt::Widgets — none
  of the surviving translation units reach for them.

Build flag plumbing:
- BUILD_BONSAIVIEWER now auto-enables BUILD_BONSAIVIEWER_WGPU since
  SceneLoader requires the wgpu lib for its WgpuViewportWindow* arg.
- The wgpu subprojects add_subdirectory ahead of the GL one so
  IfcViewerWgpu exists when IfcViewer's link evaluates.
- src/ifcviewer-minimal subdir reference removed from cmake/CMakeLists.

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

src/bonsaiviewer/modules/viewport/Commands.cpp

@@ -22,11 +22,11 @@
 
 #include "../../SessionState.h"
 #include "../../../ifcviewer/Federation.h"
-#include "../../../ifcviewer/ViewportWindow.h"
+#include "../../../ifcviewer-wgpu/WgpuViewportWindow.h"
 
 namespace bonsaiviewer::modules::viewport::commands {
 
-void setHome(SessionState& session, ViewportWindow& vp) {
+void setHome(SessionState& session, WgpuViewportWindow& vp) {
     auto camera = vp.cameraState();
     Federation::HomeView home_view;
     home_view.target = camera.target;
@@ -37,7 +37,7 @@ void setHome(SessionState& session, ViewportWindow& vp) {
     session.setStatusMessage("Camera", "Home view updated");
 }
 
-void goHome(SessionState& session, ViewportWindow& vp) {
+void goHome(SessionState& session, WgpuViewportWindow& vp) {
     Federation* federation = session.federation();
     if (!federation->hasHomeView()) {
         session.setStatusMessage("Camera", "No home view set for this project");
@@ -50,52 +50,52 @@ void goHome(SessionState& session, ViewportWindow& vp) {
     session.setStatusMessage("Camera", "Home view restored");
 }
 
-void viewSelected(ViewportWindow& vp) {
+void viewSelected(WgpuViewportWindow& vp) {
     vp.focusOnSelectedObject();
 }
 
-void fly(SessionState& session, ViewportWindow& vp) {
+void fly(SessionState& session, WgpuViewportWindow& vp) {
     vp.requestActivate();
     vp.enterFpsMode();
     session.setStatusMessage("Mode", "Fly mode active");
 }
 
-void toggleSection(SessionState& session, ViewportWindow& vp) {
+void toggleSection(SessionState& session, WgpuViewportWindow& vp) {
     vp.toggleSectionTool();
     session.setStatusMessage("Section",
         vp.sectionToolActive() ? "Section tool active" : "Section tool off");
 }
 
-void clearSection(SessionState& session, ViewportWindow& vp) {
+void clearSection(SessionState& session, WgpuViewportWindow& vp) {
     vp.clearSectionPlanes();
     session.setStatusMessage("Section", "Section planes cleared");
 }
 
-void toggleDistance(ViewportWindow& vp) {
+void toggleDistance(WgpuViewportWindow& vp) {
     vp.toggleLengthTool();
 }
 
-void toggleArea(ViewportWindow& vp) {
+void toggleArea(WgpuViewportWindow& vp) {
     vp.toggleAreaTool();
 }
 
-void toggleVolume(ViewportWindow& vp) {
+void toggleVolume(WgpuViewportWindow& vp) {
     vp.toggleVolumeTool();
 }
 
-void hideSelected(ViewportWindow& vp) {
+void hideSelected(WgpuViewportWindow& vp) {
     vp.hideSelectedElements();
 }
 
-void isolateSelected(ViewportWindow& vp) {
+void isolateSelected(WgpuViewportWindow& vp) {
     vp.isolateSelectedElements();
 }
 
-void showAll(ViewportWindow& vp) {
+void showAll(WgpuViewportWindow& vp) {
     vp.showAllElements();
 }
 
-void invertVisibility(ViewportWindow& vp) {
+void invertVisibility(WgpuViewportWindow& vp) {
     vp.invertElementVisibility();
 }