✨ add ZoomMouseScene with zoom-to-mouse correction

Implements scroll correction after cam.setZoom() so the world point
under the mouse stays fixed. Formula accounts for Phaser's
center-based zoom: scrollX += (mouseX - cw/2) * (1/zBefore - 1/zAfter).
Tab switches between the two test scenes in both directions.
Also fixes centerWorld formula in ZoomTestScene overlay and logs.

src/test/main.ts

@@ -1,12 +1,13 @@
 import Phaser from 'phaser'
 import { ZoomTestScene } from './ZoomTestScene'
+import { ZoomMouseScene } from './ZoomMouseScene'
 
 const config: Phaser.Types.Core.GameConfig = {
   type: Phaser.AUTO,
   width: window.innerWidth,
   height: window.innerHeight,
   backgroundColor: '#0d1a0d',
-  scene: [ZoomTestScene],
+  scene: [ZoomTestScene, ZoomMouseScene],
   scale: {
     mode: Phaser.Scale.RESIZE,
     autoCenter: Phaser.Scale.CENTER_BOTH,