fix: SVA chapters

app/books/sva/page.tsx

@@ -12,7 +12,7 @@ export default async function SvaPage() {
 
   const introSegments = await getSvaIntroSegments();
 
-  // Split intro segments into front matter (order < 99) and back matter (order >= 99)
+  // Split intro segments into front matter (before chapters) and back matter (after)
   const frontMatter = introSegments.filter((seg) => seg.order < 99);
   const backMatter = introSegments.filter((seg) => seg.order >= 99);
 
@@ -69,35 +69,32 @@ export default async function SvaPage() {
           </div>
         )}
 
-        {/* Chapters (Parts) */}
-        <div>
-          <h2 className="text-sm font-bold uppercase tracking-wider text-muted-foreground mb-3">
-            Parts
-          </h2>
-          <Card className="divide-y divide-border">
-            <CardContent className="p-0">
-              <ul className="divide-y divide-border">
-                {meta.chapters.map((ch) => (
-                  <li key={ch.number}>
-                    <Link
-                      href={`/books/sva/${ch.number}`}
-                      className="flex flex-col sm:flex-row sm:items-center sm:justify-between px-5 py-4 gap-1 sm:gap-0 hover:bg-muted transition-colors"
-                    >
-                      <div>
-                        <span className="text-sm text-primary font-medium">
-                          Part {ch.number}
-                        </span>
+        {/* Parts — hierarchical parent → song (sub-chapter) structure */}
+        {meta.chapters.map((ch) => (
+          <div key={ch.number}>
+            <h2 className="text-sm font-bold uppercase tracking-wider text-muted-foreground mb-3">
+              Part {ch.number}: {ch.title}
+            </h2>
+            <Card className="divide-y divide-border">
+              <CardContent className="p-0">
+                <ul className="divide-y divide-border">
+                  {ch.subChapters.map((sub) => (
+                    <li key={sub.slug}>
+                      <Link
+                        href={`/books/sva/${sub.slug}`}
+                        className="flex flex-col sm:flex-row sm:items-center sm:justify-between px-5 py-4 gap-1 sm:gap-0 hover:bg-muted transition-colors"
+                      >
                         <p className="font-medium text-foreground">
-                          {ch.title}
+                          {sub.title}
                         </p>
-                      </div>
-                    </Link>
-                  </li>
-                ))}
-              </ul>
-            </CardContent>
-          </Card>
-        </div>
+                      </Link>
+                    </li>
+                  ))}
+                </ul>
+              </CardContent>
+            </Card>
+          </div>
+        ))}
 
         {/* Back Matter */}
         {backMatter.length > 0 && (