fix: Convert OG image from SVG to PNG for Twitter/social card support

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vveerrgg

docs/index.html

@@ -11,7 +11,7 @@
     <meta property="og:url" content="https://nostrkey.com/">
     <meta property="og:title" content="NostrKey - Cross-Browser Nostr Key Management">
     <meta property="og:description" content="Secure Nostr key management for Chrome, Safari, and iOS. NIP-07 signing, encrypted vault, and nsecBunker support.">
-    <meta property="og:image" content="https://nostrkey.com/og-image.svg">
+    <meta property="og:image" content="https://nostrkey.com/og-image.png">
     <meta property="og:image:width" content="1200">
     <meta property="og:image:height" content="630">
 
@@ -20,7 +20,7 @@
     <meta name="twitter:url" content="https://nostrkey.com/">
     <meta name="twitter:title" content="NostrKey - Cross-Browser Nostr Key Management">
     <meta name="twitter:description" content="Secure Nostr key management for Chrome, Safari, and iOS. NIP-07 signing, encrypted vault, and nsecBunker support.">
-    <meta name="twitter:image" content="https://nostrkey.com/og-image.svg">
+    <meta name="twitter:image" content="https://nostrkey.com/og-image.png">
 
     <!-- Favicon -->
     <link rel="icon" type="image/svg+xml" href="data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 100 100'><circle cx='50' cy='50' r='45' stroke='%23a6e22e' stroke-width='4' fill='%233e3d32'/><path d='M35 50L45 60L65 40' stroke='%23a6e22e' stroke-width='6' stroke-linecap='round' stroke-linejoin='round' fill='none'/></svg>">