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

@@ -1,16 +1,6 @@
 @inherits LayoutComponentBase
-<div class="page">
-    <div class="sidebar">
-        <NavMenu />
-    </div>
-
+<div class="main-container">
     <main>
-        <div class="top-row px-4">
-            <a href="https://learn.microsoft.com/aspnet/core/" target="_blank">About</a>
-        </div>
-
-        <article class="content px-4">
-            @Body
-        </article>
+        @Body
     </main>
 </div>