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/MainWindow.h

@@ -0,0 +1,121 @@
+/********************************************************************************
+ *                                                                              *
+ * 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/>.         *
+ *                                                                              *
+ ********************************************************************************/
+
+#ifndef MAINWINDOW_H
+#define MAINWINDOW_H
+
+#include <QMainWindow>
+#include <QTreeWidget>
+#include <QTableWidget>
+#include <QProgressBar>
+#include <QLabel>
+#include <QSplitter>
+#include <QTimer>
+#include <QElapsedTimer>
+
+#include <map>
+#include <deque>
+#include <thread>
+#include <unordered_map>
+
+#include "ViewportWindow.h"
+#include "GeometryStreamer.h"
+
+class SettingsWindow;
+
+using ModelId = uint32_t;
+
+struct ModelHandle {
+    ModelId id = 0;
+    QString file_path;
+    QString display_name;
+    GeometryStreamer* streamer = nullptr;
+    QTreeWidgetItem* tree_root = nullptr;
+    bool visible = true;
+};
+
+class MainWindow : public QMainWindow {
+    Q_OBJECT
+public:
+    explicit MainWindow(QWidget* parent = nullptr);
+    ~MainWindow();
+
+    void addFiles(const QStringList& paths);
+    void setPendingCamera(const QString& params);
+    void setPendingBenchmark(int frames);
+
+private slots:
+    void onFileOpen();
+    void onFileSettings();
+    void onProgressChanged(int percent);
+    void onMeshReady(MeshChunk chunk);
+    void onInstanceReady(InstanceChunk chunk);
+    void onStreamingFinished();
+    void onObjectPicked(uint32_t object_id);
+    void onTreeSelectionChanged();
+    void pollNewElements();
+
+private:
+    void setupUi();
+    void setupMenus();
+    void populateProperties(uint32_t object_id);
+    void startNextLoad();
+    void applySidecarData(ModelId mid, SidecarData data);
+    void joinSidecarThread();
+    void populateTreeFromSidecar(ModelHandle& model,
+                                 const std::vector<PackedElementInfo>& elements,
+                                 const std::string& string_table);
+    void connectStreamer(GeometryStreamer* streamer);
+
+    ViewportWindow* viewport_ = nullptr;
+    SettingsWindow* settings_ = nullptr;
+    QWidget* viewport_container_ = nullptr;
+    QTreeWidget* element_tree_ = nullptr;
+    QTableWidget* property_table_ = nullptr;
+    QProgressBar* progress_bar_ = nullptr;
+    QLabel* status_label_ = nullptr;
+    QLabel* stats_label_ = nullptr;
+    QTimer element_poll_timer_;
+    QElapsedTimer load_timer_;
+
+    // Multi-model state
+    std::map<ModelId, ModelHandle> models_;
+    ModelId next_model_id_ = 1;
+    uint32_t next_object_id_ = 1; // monotonically increasing across all models
+    std::deque<ModelId> load_queue_;
+    ModelId loading_model_id_ = 0;
+    std::thread sidecar_read_thread_;
+
+    // Map object_id -> tree item and element info
+    std::unordered_map<uint32_t, ElementInfo> element_map_;
+    std::unordered_map<uint32_t, QTreeWidgetItem*> tree_items_;
+    // Scoped (model_id, ifc_id) -> object_id
+    std::unordered_map<uint64_t, uint32_t> scoped_ifc_id_to_object_id_;
+
+    static uint64_t scopedKey(uint32_t model_id, int ifc_id) {
+        return (static_cast<uint64_t>(model_id) << 32) | static_cast<uint32_t>(ifc_id);
+    }
+
+    QString pending_camera_;
+    int     pending_benchmark_ = 0;
+
+    void applyPendingBenchmark();
+};
+
+#endif // MAINWINDOW_H