fix(seo): use body H1 as case-file <title> and OG title

generateMetadata still derived the page <title>/OG title from the generic
auto frontmatter topic ("Dow Uap D44 …"). Search engines, link cards, and
AI crawlers show that string, so it must be the human magazine headline the
narrator wrote as the body H1. Mirror the page component's H1 extraction.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/app/c/[slug]/page.tsx

@@ -81,7 +81,14 @@ export async function generateMetadata(
   const c = await loadCase(slug);
   if (!c) return { title: "Case file not found" };
 
-  const title = locale === "pt-br" ? (c.fm.topic_pt_br ?? c.fm.topic ?? slug) : (c.fm.topic ?? slug);
+  // Prefer the narrator's body H1 (the magazine headline) over the generic
+  // auto-derived frontmatter topic ("Dow Uap D44 …"). This is what search
+  // engines and link cards show, so it must be the human title. Two H1s when
+  // present: EN then PT-BR; fall back across them, then to frontmatter.
+  const h1s = [...c.body.matchAll(/^#\s+(.+)$/gm)].map((m) => m[1].trim());
+  const title = locale === "pt-br"
+    ? (h1s[1] ?? h1s[0] ?? c.fm.topic_pt_br ?? c.fm.topic ?? slug)
+    : (h1s[0] ?? c.fm.topic ?? slug);
   const desc = pickLead(c.body, locale).slice(0, 200);
   const canonical = `${SITE_URL}/c/${slug}`;
   // OG image — use the case's editorial illustration when present. WhatsApp,