fix AI comment interpolation, add chapter index redirects

Use Fragment set:html for the AI-facing HTML comment so template
expressions are actually interpolated. Add index routes for
/chapters/[chapter]/ and /chapters/[version]/[chapter]/ that
redirect to the first section.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Félix Dorn

src/pages/chapters/[chapter]/index.astro

@@ -0,0 +1,37 @@
+---
+import type { Chapter } from '@/textbook-loader';
+import { getTextbooks } from "@/lib/textbooks";
+
+export async function getStaticPaths() {
+  const textbooks = await getTextbooks();
+  const sorted = textbooks.sort((a, b) => b.data.version.localeCompare(a.data.version));
+  if (sorted.length === 0) return [];
+  const textbook = sorted[0];
+
+  let paths = []
+
+  for (const chapter of textbook.data.chapters) {
+    const chapterVariants = [
+      String(chapter.number),
+      String(chapter.number).padStart(2, '0'),
+      chapter.slug,
+    ];
+
+    for (const chapterParam of chapterVariants) {
+      paths.push({
+        params: { chapter: chapterParam },
+        props: {
+          version: textbook.data.version,
+          chapter,
+        },
+      })
+    }
+  }
+
+  return paths
+}
+
+const { version, chapter } = Astro.props as { version: string; chapter: Chapter };
+
+return Astro.redirect(`/chapters/${version}/${chapter.slug}/${chapter.sections[0].slug}`, 301);
+---

src/pages/chapters/[version]/[chapter]/[section].astro

@@ -68,22 +68,22 @@ const chapterMarkdownUrl = `/chapters/${version}/${chapter.slug}.md`;
 const lecture = resolveResource(chapter.meta.lecture);
 const paper = resolveResource(chapter.meta.paper);
 ---
-<!--
+<Fragment set:html={`<!--
     AI Safety Atlas — the open textbook for AI Safety
     Published by the French Center for AI Safety (CeSIA)
     https://ai-safety-atlas.com
 
-    This page: Chapter {chapter.number}, Section {section.number} — {section.title}
-    Authors: {chapter.meta.authors.map(a => a.name).join(', ')}
-    Version: {version}
+    This page: Chapter ${chapter.number}, Section ${section.number} — ${section.title}
+    Authors: ${chapter.meta.authors.map(a => a.name).join(', ')}
+    Version: ${version}
 
     Machine-readable formats:
-      Markdown (this section): {sectionMarkdownUrl}
-      Markdown (full chapter): {chapterMarkdownUrl}
+      Markdown (this section): ${sectionMarkdownUrl}
+      Markdown (full chapter): ${chapterMarkdownUrl}
 
     Append .md to any section or chapter URL to get clean markdown.
-    Citation: {siteConfig.citation}
--->
+    Citation: ${siteConfig.citation}
+-->`} />
 <Reader title={`${section.title} - Chapter ${chapter.number}`} description="" activeSection={section} textbook={textbook} markdownUrl={sectionMarkdownUrl} breadcrumbs={[
     { text: `Chapter ${chapter.number}`, url: `/chapters/${version}/${chapter.slug}/${chapter.sections[0].slug}` },
     { text: section.title, url: '#' }

src/pages/chapters/[version]/[chapter]/index.astro

@@ -0,0 +1,30 @@
+---
+import type { Chapter } from '@/textbook-loader';
+import { getTextbooks } from "@/lib/textbooks";
+
+export async function getStaticPaths() {
+  const textbooks = await getTextbooks();
+  let paths = []
+
+  for (const textbook of textbooks) {
+    for (const chapter of textbook.data.chapters) {
+      paths.push({
+        params: {
+          version: textbook.data.version,
+          chapter: chapter.slug,
+        },
+        props: {
+          version: textbook.data.version,
+          chapter,
+        },
+      })
+    }
+  }
+
+  return paths
+}
+
+const { version, chapter } = Astro.props as { version: string; chapter: Chapter };
+
+return Astro.redirect(`/chapters/${version}/${chapter.slug}/${chapter.sections[0].slug}`, 301);
+---