fix issue where upgrade modules are not working properly

src/lib/sim/ShipStatsCalculator.cpp

@@ -157,6 +157,22 @@ ShipStats calculateShipStats(const GameConfig& config,
         }
     }
 
+    // Acceleration additive modifiers are in m/s² in config; convert to tiles/s².
+    const char* const kAccelerationStats[] = {
+        "main_acceleration", "maneuvering_acceleration"
+    };
+    for (const char* stat : kAccelerationStats)
+    {
+        for (std::map<std::string, std::pair<double, double>>* mods : allModMaps)
+        {
+            std::map<std::string, std::pair<double, double>>::iterator it = mods->find(stat);
+            if (it != mods->end())
+            {
+                it->second.second /= tileSize;
+            }
+        }
+    }
+
     auto applyMod = [](float& stat, const std::string& name,
                        const std::map<std::string, std::pair<double, double>>& mods)
     {