Footer quotes + right-hand table of contents

- two static quotes above the name line in every footer
- Toc component renders h1-h3 from Astro's render() headings as a sticky
  right column on >=88rem screens (hidden below); scroll-position
  highlighting via a small passive listener; shown only when a page has
  2+ headings, so listings and short notes stay clean

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/pages/[...slug].astro

@@ -59,10 +59,15 @@ const { entry, listing } = Astro.props;
 const title = entry
   ? (entry.data.title ?? entry.id.split('/').pop())
   : listing.name;
-const Content = entry ? (await render(entry)).Content : null;
+const rendered = entry ? await render(entry) : null;
+const Content = rendered?.Content ?? null;
 ---
 
-<Base title={title} description={entry?.data.description}>
+<Base
+  title={title}
+  description={entry?.data.description}
+  headings={rendered?.headings ?? []}
+>
   <h1>{title}</h1>
   {Content && <Content />}
   {