Fix scene selector init and start game on load

main.js

@@ -127,6 +127,7 @@
   const paletteLegendEl = document.getElementById("palette-legend");
   const scoreEl = document.getElementById("score");
   const highScoreEl = document.getElementById("high-score");
+  const sceneSelectEl = document.getElementById("scene-select");
   const gameOverEl = document.getElementById("game-over");
   const finalScoreEl = document.getElementById("final-score");
   const restartBtn = document.getElementById("restart-btn");
@@ -166,7 +167,6 @@
     boundaries = currentScene.createBodies(width, height);
     World.add(world, boundaries);
   };
-  rebuildSceneBodies();
 
   const balls = [];
   let spawnTimer = null;
@@ -196,6 +196,7 @@
   };
 
   const populateSceneSelect = () => {
+    if (!sceneSelectEl) return;
     sceneSelectEl.innerHTML = "";
     scenes.forEach((scene) => {
       const opt = document.createElement("option");
@@ -208,7 +209,7 @@
   const applyScene = (sceneId) => {
     const next = scenes.find((s) => s.id === sceneId) || scenes[0];
     currentScene = next;
-    sceneSelectEl.value = next.id;
+    if (sceneSelectEl) sceneSelectEl.value = next.id;
     Object.assign(config, next.config);
     engine.gravity.y = config.gravity;
     rebuildSceneBodies();
@@ -579,11 +580,10 @@
       setPaused(!isPaused);
     }
   });
+  if (sceneSelectEl) {
     sceneSelectEl.addEventListener("change", (e) => applyScene(e.target.value));
-  populateSceneSelect();
-  sceneSelectEl.value = currentScene.id;
+  }
   highScore = loadHighScore();
-  buildLegend();
-  updateHud();
-  startSpawner();
+  populateSceneSelect();
+  applyScene(currentScene.id);
 })();