feat(post-page): separate headline and body content for improved rendering

- Extracted headline and body content from the post's HTML, allowing for distinct rendering of the headline and body in the post page.
- Updated the Svelte component to display the extracted headline and body content separately, enhancing the layout and readability of posts.

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

@@ -76,6 +76,14 @@ export const load: PageServerLoad = async ({ params, locals, url }) => {
     contentHtml = await processMarkdownHtmlImages(contentHtml);
   }
 
+  let contentHeadlineHtml = '';
+  let contentBodyHtml = contentHtml;
+  const h1Match = contentHtml.match(/^\s*(<h1\b[^>]*>[\s\S]*?<\/h1>)([\s\S]*)$/);
+  if (h1Match) {
+    contentHeadlineHtml = h1Match[1];
+    contentBodyHtml = h1Match[2];
+  }
+
   const hasRowContent =
     ((post as { row1Content?: unknown[] }).row1Content?.length ?? 0) > 0 ||
     ((post as { row2Content?: unknown[] }).row2Content?.length ?? 0) > 0 ||
@@ -199,6 +207,8 @@ export const load: PageServerLoad = async ({ params, locals, url }) => {
     postImageFocal: postImageField?.focal ?? null,
     postDate,
     contentHtml,
+    contentHeadlineHtml,
+    contentBodyHtml,
     hasRowContent,
     isEvent,
     eventDateRaw,