docs: do not consider the main title as part of ToC (#9699)

This makes sure we don't double show the description of the page when at
the top.

Author: jd

src/components/PageContent/PageContent.astro

@@ -32,7 +32,9 @@ const suppressTitle = content.suppressTitle;
 			<header>
 				<slot name="before-title" />
 				{!suppressTitle && <h1 class="content-title" id="overview" set:html={title} />}
-				{!suppressTitle && <h2 class="content-subtitle" set:html={description} />}
+				{!suppressTitle && (
+					<h2 class="content-subtitle" data-toc-ignore set:html={description} />
+				)}
 				<slot name="after-title" />
 			</header>
 			{!suppressTitle && <hr class="divider" />}

src/components/RightSidebar/TableOfContents.tsx

@@ -87,8 +87,10 @@ const TableOfContents = ({ toc = [], labels, isMobile }: Props) => {
 
     const headingsObserver = new IntersectionObserver(setCurrent, observerOptions);
 
-    // Observe all the headings in the main page content.
-    document.querySelectorAll('article :is(h1,h2,h3)').forEach((h) => headingsObserver.observe(h));
+    // Observe all the headings in the main page content, skipping ones marked to ignore.
+    document
+      .querySelectorAll('article :is(h1,h2,h3):not([data-toc-ignore])')
+      .forEach((h) => headingsObserver.observe(h));
 
     // Stop observing when the component is unmounted.
     return () => headingsObserver.disconnect();