style: Add responsive viewport meta tag and css rules

frontend/index.html

@@ -8,6 +8,7 @@
     <link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png" />
     <meta name="apple-mobile-web-app-title" content="MyTube" />
     <link rel="manifest" href="/site.webmanifest" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
     <meta name="theme-color" content="#ff3e3e" />
     <title>MyTube - Download & Watch YouTube Videos</title>
   </head>

frontend/src/index.css

@@ -7,6 +7,13 @@ body {
   margin: 0;
   padding: 0;
   box-sizing: border-box;
+  width: 100%;
+  overflow-x: hidden;
+}
+
+html {
+  width: 100%;
+  overflow-x: hidden;
 }
 
 /* Scrollbar styling for dark theme */