feat: update to react 19, pixi.js v8, tailwind v4, shad-cn

Also:

- center canvas on startup
- add version 1.21.9

postcss.config.js

@@ -1,6 +1,5 @@
 export default {
   plugins: {
-    tailwindcss: {},
-    autoprefixer: {},
+    '@tailwindcss/postcss': {},
   },
 }