fix(webgl): use forceCanvas for Live2DCat to avoid dual WebGL context conflicts

Reverts shared-context approach. Live2DCat gets its own canvas with
forceCanvas:true (Canvas2D renderer), which avoids the WebGL bindBuffer
spam entirely. Cleaned up onAppReady prop from KiraAvatar.

frontend/src/components/KiraAvatar.tsx

@@ -7,7 +7,6 @@ interface Props {
   outfit: string;
   accessory: string | null;
   onTalkToggle: () => void;
-  onAppReady?: (app: any) => void;
 }
 
 type ExpressionName = 'Normal' | 'Smile' | 'Sad' | 'Angry' | 'Surprised' | 'Blushing';
@@ -82,8 +81,7 @@ export default function KiraAvatar(props: Props) {
 
         app.stage.addChild(model as any);
         (model as any).isInteractive = () => false;
-
-        if (props.onAppReady) props.onAppReady(app);
+        if (!mounted) return;
 
         try {
           textureRef.current = {