manufacturers: rename 'Manufacturer Directory' to 'Production Industry Manufacturers'

H1, page metadata title, OG title, and the back-link on individual
manufacturer profiles all swap to the new label.

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

src/app/manufacturers/[slug]/page.tsx

@@ -167,7 +167,7 @@ export default async function ManufacturerProfile({
       <article className="max-w-4xl mx-auto px-4 py-10">
         <nav className="text-xs text-[#888] mb-6">
           <Link href="/manufacturers" className="hover:text-[#3b82f6]">
-            ← Manufacturer Directory
+            ← Production Industry Manufacturers
           </Link>
         </nav>