Add Open Graph and Twitter Card meta tags for social sharing

Uses the Darling Data barbell logo as hero image when shared on
social media. Also adds meta description for SEO.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: erikdarlingdata

src/PlanViewer.Web/wwwroot/index.html

@@ -4,6 +4,16 @@
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>Free SQL Server Query Plan Analysis — Darling Data</title>
+    <meta name="description" content="Free browser-based SQL Server execution plan analysis. Paste or upload a .sqlplan file — your plan XML never leaves your browser." />
+    <meta property="og:title" content="Free SQL Server Query Plan Analysis" />
+    <meta property="og:description" content="Paste or upload a .sqlplan file. Your plan XML never leaves your browser." />
+    <meta property="og:image" content="https://plans.erikdarling.com/darling-data-logo.jpg" />
+    <meta property="og:url" content="https://plans.erikdarling.com" />
+    <meta property="og:type" content="website" />
+    <meta name="twitter:card" content="summary_large_image" />
+    <meta name="twitter:title" content="Free SQL Server Query Plan Analysis" />
+    <meta name="twitter:description" content="Paste or upload a .sqlplan file. Your plan XML never leaves your browser." />
+    <meta name="twitter:image" content="https://plans.erikdarling.com/darling-data-logo.jpg" />
     <link rel="icon" type="image/png" href="favicon.png" />
     <base href="/" />
     <link rel="preconnect" href="https://fonts.googleapis.com" />