feat(site): add pre-release docs banner on main.videojs.org (#1575)

site/src/components/PrereleaseBanner.astro

@@ -0,0 +1,32 @@
+---
+import { isPrereleaseSite, PRODUCTION_URL } from '@/consts';
+
+// Only render on the pre-release host. Evaluated at build time, so the markup
+// is omitted entirely from production and deploy-preview builds.
+const showBanner = isPrereleaseSite(Astro.site);
+---
+
+{
+  showBanner && (
+    <div
+      role="region"
+      aria-label="Pre-release documentation notice"
+      class:list={[
+        "py-2 text-p3 md:text-p2",
+        "border-b border-manila-75 bg-manila-50 text-faded-black",
+        "dark:border-soot dark:bg-warm-gray dark:text-manila-light",
+      ]}
+    >
+      <p class="text-center">
+        You&rsquo;re viewing pre-release docs.{" "}
+        <a
+          href={PRODUCTION_URL.href}
+          class="font-bold whitespace-nowrap underline intent:decoration-gold"
+        >
+          Visit videojs.org
+        </a>{" "}
+        for the latest stable version.
+      </p>
+    </div>
+  )
+}