refactor: update Geant scene visualization to use PhysicalVolumes instead of raw Solids for improved placement and context handling.

src/HEP/Geant/Scene.cpp

@@ -127,6 +127,10 @@ const Vector<Solid*>& Scene::GetSolids() const {
     return d->m_Solids; 
 }
 
+const Vector<SmartPointer<PhysicalVolume>>& Scene::GetVolumes() const {
+    return d->m_Volumes;
+}
+
 void Scene::ConstructWorldBox(const Vector3f &size, const char *materialName) {
   d->m_WorldBox->SetSize(size);
 

src/HEP/Geant/Scene.h

@@ -60,6 +60,9 @@ public:
   /// Get the list of solids in the scene
   const Vector<Solid*>& GetSolids() const;
 
+  /// Get the list of physical volumes in the scene
+  const Vector<SmartPointer<PhysicalVolume>>& GetVolumes() const;
+
   /// Set the primary generator (emitter) for the simulation.
   /// The Scene does NOT take ownership of the emitter.
   void SetEmitter(EmitterPrimary *emitter);