refactor: update packages to React 19, Vite 8 and Tailwind 4 and modernize configs

src/index.css

@@ -1,6 +1,21 @@
-@tailwind base;
-@tailwind components;
-@tailwind utilities;
+@import "tailwindcss";
+
+@theme {
+  --breakpoint-xs: 475px;
+  --max-width-screen-xs: 475px;
+  
+  --container-padding: 1rem;
+  --container-center: true;
+}
+
+@layer base {
+  :root {
+    --container-sm: 1.5rem;
+    --container-lg: 2rem;
+    --container-xl: 2.5rem;
+    --container-2xl: 3rem;
+  }
+}
 
 :root {
   font-family: Inter, system-ui, Avenir, Helvetica, Arial, sans-serif;