refactor: simplify CombatTestScene instantiation in App

Remove manual instantiation of CombatTestScene in favor of passing
the class directly to PhaserScene, allowing the framework to handle
scene lifecycle.

packages/sts-like-viewer/src/ui/App.tsx

@@ -12,7 +12,6 @@ import { createCombatState } from "@/state/combatState";
 import type { CombatState } from "boardgame-core/samples/slay-the-spire-like";
 
 export default function App() {
-  const combatScene = useMemo(() => new CombatTestScene(), []);
   const gameHost = useMemo(
     () => createGameHost(createCombatState() as GameModule<CombatState>),
     [],
@@ -23,11 +22,7 @@ export default function App() {
       <div className="flex-1 flex relative justify-center items-center">
         <PhaserGame initialScene="IndexScene" config={GAME_CONFIG}>
           <PhaserScene scene={IndexScene} />
-          <PhaserScene
-            sceneKey="CombatTestScene"
-            scene={combatScene}
-            data={{ gameHost }}
-          />
+          <PhaserScene scene={CombatTestScene} data={{ gameHost }} />
           <PhaserScene scene={InventoryTestScene} />
           <PhaserScene scene={MapViewerScene} />
           <PhaserScene scene={GridViewerScene} />