feat(post): emit VideoObject JSON-LD for embedded YouTube videos

Posts whose row*Content contains a `youtube_video` block now ship a
schema.org VideoObject per video alongside the existing BlogPosting /
Event JSON-LD. Lets Google attach a video rich-result to the post URL
(thumbnail, duration where available, embed/content URLs) instead of
treating the page as plain text whose body happens to be a single
iframe.

Thumbnail uses YouTube's predictable maxresdefault + hqdefault URLs;
upload date falls back to post.created when the embed has none.

src/routes/post/[slug]/+page.server.ts

@@ -171,6 +171,43 @@ export const load: PageServerLoad = async ({ params, locals, url, setHeaders })
   };
   jsonLd.push(articleLd);
 
+  // Collect YouTube embeds from row*Content and emit a VideoObject per video.
+  // Helps Google index the post as a video page (rich result eligibility).
+  type RowItem = { _type?: string; youtubeId?: string; title?: string; description?: string };
+  const rows: RowItem[] = [
+    ...(((post as { row1Content?: RowItem[] }).row1Content) ?? []),
+    ...(((post as { row2Content?: RowItem[] }).row2Content) ?? []),
+    ...(((post as { row3Content?: RowItem[] }).row3Content) ?? []),
+  ];
+  const videos = rows.filter(
+    (r) => r && r._type === 'youtube_video' && typeof r.youtubeId === 'string' && r.youtubeId,
+  );
+  for (const v of videos) {
+    const id = v.youtubeId as string;
+    jsonLd.push({
+      '@context': 'https://schema.org',
+      '@type': 'VideoObject',
+      name: v.title ?? postHeadline,
+      description: v.description ?? postDescription ?? postHeadline,
+      thumbnailUrl: [
+        `https://i.ytimg.com/vi/${id}/maxresdefault.jpg`,
+        `https://i.ytimg.com/vi/${id}/hqdefault.jpg`,
+      ],
+      uploadDate: postCreated ?? new Date().toISOString(),
+      contentUrl: `https://www.youtube.com/watch?v=${id}`,
+      embedUrl: `https://www.youtube.com/embed/${id}`,
+      ...(siteBaseUrl
+        ? {
+            publisher: {
+              '@type': 'Organization',
+              name: siteName,
+              url: siteBaseUrl,
+            },
+          }
+        : {}),
+    });
+  }
+
   if (isEvent && eventDateRaw) {
     const eventLd: Record<string, unknown> = {
       '@context': 'https://schema.org',