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/lib/site.ts

@@ -17,11 +17,24 @@ export const GITHUB_URL = 'https://github.com/Azzamo-net/cashumints.space';
 export const AZZAMO_URL = 'https://azzamo.net';
 
 /**
- * The default social card, served from `public/`.
+ * The default social card: brand, tagline and the network's stats, rendered by
+ * `pnpm og` into `public/og/` alongside the per-mint cards. Home, the list pages and
+ * any mint whose own card failed to render all point here.
  *
  * Relative on purpose: `Base.astro` resolves it against `Astro.site`, because an
  * `og:image` that is not absolute is not a weaker signal, it is an ignored one.
+ * Stable filename, unlike the hashed per-mint cards, so it is served with
+ * `Cache-Control: max-age=3600` rather than immutable (see README).
  */
-export const OG_IMAGE = '/og.png';
+export const OG_IMAGE = '/og/default.png';
 export const OG_IMAGE_WIDTH = 1200;
 export const OG_IMAGE_HEIGHT = 630;
+
+/**
+ * Whether a rated mint's JSON-LD also carries the review-snippet-eligible `Product`
+ * type (see `mintServiceNode` in schema.ts for the reasoning). On by default; set
+ * `SEO_PRODUCT_JSONLD=0` to fall back to the plain `Service` node on the next build.
+ * An env flag rather than a source edit, so the call can be reversed without a code
+ * change if Google's treatment of self-collected review markup shifts.
+ */
+export const PRODUCT_JSONLD = (process.env['SEO_PRODUCT_JSONLD'] ?? '1') !== '0';