refactor: Optimize terrain rendering and zooming performance

terrain.js

@@ -182,6 +182,7 @@ function isWater(x, y) {
 // Get terrain type at a position
 function getTerrainType(x, y) {
   // Convert world coordinates to terrain grid coordinates
+  // Use consistent rounding to prevent shaking
   const gridX = Math.floor((x + 2000) / 10);
   const gridY = Math.floor((y + 2000) / 10);