chore: better meta tags for link previews

src/layouts/BaseLayout.astro

@@ -31,7 +31,9 @@ const { title, description, thumbnail, pageTags } = Astro.props
 
         <meta property="og:title" content={title ?? 'PHC'} />
         <meta property="og:description" content={description ?? 'Sito web del PHC'} />
+        <meta name="description" content={description ?? 'Sito web del PHC'} />
         <meta property="og:type" content="website" />
+        <meta property="og:url" content="https://phc.dm.unipi.it/" />
         {thumbnail && <meta property="og:image" content={thumbnail} />}
 
         <link rel="icon" type="image/png" sizes="512x512" href="/favicon.svg" />