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/tsconfig.tsbuildinfo

@@ -0,0 +1 @@
+{"root":["./src/App.tsx","./src/main.tsx","./src/vite-env.d.ts","./src/components/AnimatedAvatar.tsx","./src/components/BackgroundScene.tsx","./src/components/ChatBubble.tsx","./src/components/Clock.tsx","./src/components/KiraAvatar.tsx","./src/components/MusicPlayer.tsx","./src/components/Notes.tsx","./src/components/Particles.tsx","./src/components/PetZone.tsx","./src/components/Timer.tsx","./src/components/Toolbar.tsx","./src/components/Wardrobe.tsx","./src/components/WelcomeScreen.tsx","./src/components/scenes.ts","./src/hooks/useConversation.ts","./src/types/index.ts"],"version":"6.0.3"}