feat: Monero coin favicon with paid indicator

- Official Monero coin logo as SVG favicon
- Dynamic green dot badge on favicon when invoice is paid
- Paid status shown both in page content and browser tab

index.html

@@ -5,7 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>xmrpay.link — Monero Invoice Generator</title>
   <meta name="description" content="Create Monero payment requests in seconds. No account, no backend, no KYC.">
-  <link rel="icon" href="data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 100 100'><text y='.9em' font-size='90'>⛏️</text></svg>">
+  <link rel="icon" id="favicon" href="favicon.svg" type="image/svg+xml">
   <link rel="preconnect" href="https://fonts.googleapis.com">
   <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;600;700&family=JetBrains+Mono:wght@400&display=swap" rel="stylesheet">
   <link rel="stylesheet" href="style.css">