fix: TypeScript build errors in Docker

- useRef(null) initial values for Strict TS 6.0
- Removed deprecated transparent option in pixi v7
- Cast Live2DModel to any for addChild type compat
- Cast coreModel for getTexture access
- Fixed types/index.ts import path to scenes
- Added vite-env.d.ts with CSS module declarations
- Added null-coalesce for clearInterval calls

frontend/src/components/KiraAvatar.tsx

@@ -28,7 +28,7 @@ export default function KiraAvatar(props: Props) {
   const modelRef = useRef<any>(null);
   const textureRef = useRef<any>(null);
   const lipSyncRef = useRef<number>(0);
-  const idleExprRef = useRef<ReturnType<typeof setInterval>>();
+  const idleExprRef = useRef<ReturnType<typeof setInterval> | null>(null);
   const [live2dReady, setLive2dReady] = useState(false);
   const [loadError, setLoadError] = useState(false);
   const [currentExpression, setCurrentExpression] = useState<ExpressionName>('Normal');
@@ -56,7 +56,6 @@ export default function KiraAvatar(props: Props) {
         const app = new Application({
           width: size,
           height: size * 1.25,
-          transparent: true,
           antialias: true,
           resolution: Math.min(window.devicePixelRatio || 1, 2),
           backgroundAlpha: 0,
@@ -80,13 +79,13 @@ export default function KiraAvatar(props: Props) {
         model.anchor.set(0.5, 0.5);
         model.position.set(app.screen.width / 2, app.screen.height / 2 + 6);
 
-        app.stage.addChild(model);
+        app.stage.addChild(model as any);
 
         // Store reference to texture_02 for outfit swapping
         try {
           textureRef.current = {
             index: 2,
-            original: model.internalModel.coreModel.getTexture(2),
+            original: (model.internalModel.coreModel as any).getTexture(2),
           };
         } catch { /* ignore */ }
 
@@ -113,7 +112,7 @@ export default function KiraAvatar(props: Props) {
     return () => {
       mounted = false;
       cancelAnimationFrame(lipSyncRef.current);
-      clearInterval(idleExprRef.current);
+      clearInterval(idleExprRef.current ?? undefined);
       if (appRef.current) {
         appRef.current.destroy(true, { children: true });
         appRef.current = null;