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/ifcviewer-minimal/main.cpp

@@ -1,70 +0,0 @@
-/********************************************************************************
- *                                                                              *
- * 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/>.         *
- *                                                                              *
- ********************************************************************************/
-
-#include <QApplication>
-#include <QSurfaceFormat>
-#include <QCommandLineParser>
-
-#include "MinimalWindow.h"
-
-int main(int argc, char* argv[]) {
-    QApplication app(argc, argv);
-    app.setApplicationName("IfcViewerMinimal");
-    app.setOrganizationName("IfcOpenShell");
-
-    QSurfaceFormat fmt;
-    fmt.setVersion(4, 5);
-    fmt.setProfile(QSurfaceFormat::CoreProfile);
-    fmt.setDepthBufferSize(24);
-    fmt.setSwapBehavior(QSurfaceFormat::DoubleBuffer);
-    fmt.setSamples(4);
-    QSurfaceFormat::setDefaultFormat(fmt);
-
-    QCommandLineParser parser;
-    parser.setApplicationDescription("IfcOpenShell minimal IFC viewer — benchmarking and debugging");
-    parser.addHelpOption();
-    parser.addPositionalArgument("files", "IFC file(s) to open", "[files...]");
-    parser.addOption({{"c", "camera"},
-        "Set camera: tx,ty,tz,dist,yaw,pitch", "params"});
-    parser.addOption({{"b", "benchmark"},
-        "Run N frames then print stats and exit", "frames"});
-    parser.addOption({{"s", "screenshot"},
-        "Render one frame after load, save to PATH as PNG, exit", "path"});
-    parser.process(app);
-
-    MinimalWindow window;
-    window.show();
-
-    auto args = parser.positionalArguments();
-    if (!args.isEmpty()) {
-        window.addFiles(args);
-    }
-
-    if (parser.isSet("camera")) {
-        window.setPendingCamera(parser.value("camera"));
-    }
-    if (parser.isSet("benchmark")) {
-        window.setPendingBenchmark(parser.value("benchmark").toInt());
-    }
-    if (parser.isSet("screenshot")) {
-        window.setPendingScreenshot(parser.value("screenshot"));
-    }
-
-    return app.exec();
-}