Improve SEO and social card wiring

Add SearchAction and optional Product JSON-LD, per-page OG images/alts, and document the og build and cache headers.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/layouts/Base.astro

@@ -57,14 +57,20 @@ interface Props {
   schema?: SchemaNode[];
   /**
    * Social card. A site-relative path, resolved to the absolute URL `og:image` requires.
-   * Defaults to the shared 1200x630 card.
+   * Defaults to the shared 1200x630 card that `pnpm og` generates.
    */
   image?: string;
+  /**
+   * Alt text for the card. Mint pages pass their own ("{name}: 4.9 stars from 54
+   * reviews…"); everything else gets the sitewide line, matching the default card.
+   */
+  imageAlt?: string;
 }
 
 const {
   title, description, current, mintCount, ogType = 'website',
   noindex = false, offGraph = false, schema = [], image = OG_IMAGE,
+  imageAlt,
 } = Astro.props;
 
 /*
@@ -217,7 +223,7 @@ const noscriptMotion =
     <meta property="og:image" content={imageUrl} />
     <meta property="og:image:width" content={String(OG_IMAGE_WIDTH)} />
     <meta property="og:image:height" content={String(OG_IMAGE_HEIGHT)} />
-    <meta property="og:image:alt" content={t('seo.ogImageAlt')} />
+    <meta property="og:image:alt" content={imageAlt ?? t('seo.ogImageAlt')} />
 
     {/*
       `summary_large_image`, now that there is an image worth the space. With no
@@ -227,7 +233,7 @@ const noscriptMotion =
     <meta name="twitter:title" content={title} />
     <meta name="twitter:description" content={description} />
     <meta name="twitter:image" content={imageUrl} />
-    <meta name="twitter:image:alt" content={t('seo.ogImageAlt')} />
+    <meta name="twitter:image:alt" content={imageAlt ?? t('seo.ogImageAlt')} />
 
     {/*
       Two faces, and only two: Inter 400 is every paragraph on the site and Space