Improve floor detection for multi-story buildings

- Increase footprint sampling radius from 0.28 to 0.4 units
- Only update floor cache if found floor is close to query height
- Prevents caching wrong floor from different stories

src/rendering/wmo_renderer.cpp

@@ -1495,8 +1495,10 @@ std::optional<float> WMORenderer::getFloorHeight(float glX, float glY, float glZ
         }
     }
 
-    // Cache the result in persistent grid (never expires)
-    if (bestFloor) {
+    // Cache the result in persistent grid.
+    // Only update cache if we found a floor that's close to query height,
+    // to avoid caching wrong floors when player is on different stories.
+    if (bestFloor && *bestFloor >= glZ - 6.0f) {
         precomputedFloorGrid[gridKey] = *bestFloor;
     }