refactor: restructure project layout

- Move source files (app.js, styles.css) to src/ directory
- Move assets (UI.webp, UI-1.webp) to assets/ directory
- Update references in index.html and README.md"

index.html

@@ -5,7 +5,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>Imagen</title>
-    <link rel="stylesheet" href="styles.css">
+    <link rel="stylesheet" href="src/styles.css">
     <link href="https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap" rel="stylesheet">
 </head>
 
@@ -161,7 +161,7 @@
         </div>
     </div>
 
-    <script src="app.js"></script>
+    <script src="src/app.js"></script>
 </body>
 
 </html>