let the world renderer hold the simulation by const reference

src/ui/WorldRenderer.h

@@ -77,7 +77,7 @@ public:
     // `itemIcons` is the window-wide per-item icon cache (REQ-UI-ITEM-ICON); not
     // owned, must outlive this renderer. `configDir` is used once, to load the
     // per-building world icons.
-    WorldRenderer(Simulation& sim, const VisualsConfig& visuals,
+    WorldRenderer(const Simulation& sim, const VisualsConfig& visuals,
                   ItemIconCache* itemIcons, const std::string& configDir);
     ~WorldRenderer();
 
@@ -141,9 +141,8 @@ private:
 
     std::optional<QVector2D> entityPosition(entt::entity entity) const;
 
-    // Non-const only because EntityAdmin's component accessors are; the renderer
-    // reads the simulation and never writes it.
-    Simulation&          m_sim;
+    // The renderer reads the simulation and never writes it.
+    const Simulation&    m_sim;
     const VisualsConfig& m_visuals;
 
     // Per-item icon cache (REQ-UI-ITEM-ICON), shared window-wide and owned by