feat(library): restore live-site intro copy above post listings

- add the two live intro paragraphs between the hero and article grid
- keep the library listing cards in the live two-column layout
- restore the 4:3 cropped article thumbnails and card spacing via library-scoped selectors
- avoid leaking the card-grid overrides into unrelated pages

www/src/layouts/BlogIndexLayout.astro

@@ -1,13 +1,18 @@
 ---
 import BaseLayout from './BaseLayout.astro';
 import PageHero from '../components/PageHero.astro';
-const { title, description, lang = 'en' } = Astro.props;
+const { title, description, intro = [], lang = 'en' } = Astro.props;
 const languagePrefix = lang === 'en' ? '' : `/${lang}`;
 const canonical = `https://www.azinstitute4autism.com${languagePrefix}/library`;
 ---
 <BaseLayout title={title} description={description} canonical={canonical} lang={lang}>
   <PageHero title={title} image="/assets/images/hero-library-index.webp" eyebrow="Welcome to" constrain />
-  <section class="library-intro"><div class="container"><h2>Library</h2><p>{description}</p></div></section>
+  <section class="library-intro">
+    <div class="container">
+      <h2>Library</h2>
+      {intro.length ? intro.map((paragraph) => <p>{paragraph}</p>) : <p>{description}</p>}
+    </div>
+  </section>
   <div class="container section library-layout"><slot /></div>
 </BaseLayout>