feat: optimize mobile viewport configuration

Add proper viewport meta tag configuration to prevent unwanted zooming and ensure optimal mobile experience with device-width scaling.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/layout.tsx

@@ -9,6 +9,12 @@ import { AppNavBar } from '@/components/AppNavBar'
 export const metadata: Metadata = {
   title: 'Soroban Flashcard Generator',
   description: 'Create beautiful, educational soroban flashcards with authentic Japanese abacus representations',
+  viewport: {
+    width: 'device-width',
+    initialScale: 1,
+    maximumScale: 1,
+    userScalable: false,
+  },
 }
 
 export default function RootLayout({