Redesign: single-page QRPay app with modern UI

Removed sidebar, Counter, and Weather pages. Rebuilt Home.razor as a focused QR payment generator with validation, responsive card layout, and QR code display. Added new CSS for modern look, updated global styles, and introduced SVG logo/favicon. Cleaned up solution and project files for a streamlined, single-page experience.

QRPay/Layout/MainLayout.razor.css

@@ -5,6 +5,8 @@
 }
 
 main {
+    width: 100%;
+    max-width: 500px;
     flex: 1;
 }
 
@@ -75,3 +77,16 @@ main {
         padding-right: 1.5rem !important;
     }
 }
+
+* {
+    box-sizing: border-box;
+}
+
+.main-container {
+    min-height: 100vh;
+    background: linear-gradient(135deg, #2d5a27 0%, #4a7c59 100%);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    padding: 20px;
+}