Fit camera to model bounding box on first render

Center the orbit controls target on the model's bounding box after
the initial evaluation so the default view frames the starter model
instead of orbiting the hardcoded origin.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: zalo

js/MainPage/CascadeView.js

@@ -134,6 +134,9 @@ class CascadeEnvironment {
     this._historyPending = false;  // True while awaiting worker mesh response
     this._lastSceneOptions = {};
 
+    // Fit camera on first render so the orbit target centers on the model
+    this._isFirstRender = true;
+
     // Register the shape rendering callback
     this._registerRenderCallback(messageBus);
 
@@ -395,6 +398,10 @@ class CascadeEnvironment {
       }
 
       this.environment.scene.add(this.mainObject);
+      if (this._isFirstRender) {
+        this._isFirstRender = false;
+        this.fitCamera();
+      }
       this.environment.viewDirty = true;
       console.log("Generation Complete!");
     });