feat: add sb front matter

app/(app)/books/sb/[canto]/page.tsx

@@ -3,8 +3,9 @@ import Link from "next/link";
 import { PageHeader } from "@/components/layout/page-header";
 import { notFound } from "next/navigation";
 import { Card, CardContent } from "@/components/ui/card";
+import { FindInPage } from "@/components/layout/find-in-page";
 import { ExtractedVerseCount } from "../../extracted-verse-count";
-import { getBookMeta } from "@/lib/api";
+import { getBookMeta, getProseChapter } from "@/lib/api";
 import { buildOgMeta } from "@/lib/og";
 import { BOOK_NAMES } from "@/lib/constants";
 
@@ -15,6 +16,11 @@ export async function generateMetadata({
 }): Promise<Metadata> {
   const { canto } = await params;
   const title = BOOK_NAMES["sb"] || "Śrīmad-Bhāgavatam";
+  // A non-numeric segment (preface, introduction) is front matter.
+  if (isNaN(parseInt(canto))) {
+    const segment = await getProseChapter("sb", 0, canto);
+    if (segment) return buildOgMeta({ title, detail: segment.title });
+  }
   return buildOgMeta({ title, detail: `Canto ${canto}` });
 }
 
@@ -38,6 +44,49 @@ export default async function CantoPage({
 }) {
   const { canto } = await params;
   const cantoNum = parseInt(canto);
+
+  // Front matter — a non-numeric param (preface, introduction) resolves to a
+  // prose intro-segment.
+  if (isNaN(cantoNum)) {
+    const segment = await getProseChapter("sb", 0, canto);
+    if (!segment) notFound();
+
+    return (
+      <div className="min-h-screen bg-background">
+        <PageHeader sticky>
+          <Link
+            href="/books/sb"
+            className="text-sm text-muted-foreground hover:text-foreground transition-colors"
+          >
+            &larr; Śrīmad-Bhāgavatam
+          </Link>
+          <div className="mt-3 flex items-start justify-between gap-3">
+            <h1 className="text-2xl font-bold text-foreground">
+              {segment.title}
+            </h1>
+            <FindInPage targetId="book-content" className="shrink-0 mt-0.5" />
+          </div>
+        </PageHeader>
+
+        <main className="max-w-5xl mx-auto px-6 py-8">
+          <Card id="book-content">
+            <CardContent className="py-8 px-6 sm:px-8">
+              <div className="space-y-4">
+                {segment.paragraphs.map((paragraph, i) => (
+                  <div
+                    key={i}
+                    className="text-base text-foreground leading-relaxed"
+                    dangerouslySetInnerHTML={{ __html: paragraph }}
+                  />
+                ))}
+              </div>
+            </CardContent>
+          </Card>
+        </main>
+      </div>
+    );
+  }
+
   const meta = await getBookMeta("sb");
   if (!meta) notFound();