manufacturer hover popup + smart back link

Content Partners (and any other) company-hover preview previously used
text-ink / bg-ink / brand-primary utilities that aren't defined in our
Tailwind config, so the popup rendered as white background with no text
color (inheriting near-white text from the dark theme parent). Replaced
every undefined utility with concrete dark-theme colors matching the rest
of the site: #111827 panel, #2a3a50 borders, #e8e8e8 body text, #60a5fa
links, real semi-transparent chip badges.

Manufacturer profile back-link now uses BackLink, a client component that
calls router.back() when we have same-origin history — so clicking the
breadcrumb from the homepage Content Partners hover returns the user to
the homepage instead of dumping them at /manufacturers. Falls through to
the directory link for new-tab opens, search-engine entries, and no-JS.

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

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

@@ -4,6 +4,7 @@ import Link from "next/link";
 import Header from "@/components/Header";
 import Footer from "@/components/Footer";
 import { createClient } from "@/lib/supabase/server";
+import BackLink from "./BackLink";
 
 export const revalidate = 1800;
 
@@ -166,9 +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]">
-            ← Production Industry Manufacturers
-          </Link>
+          <BackLink />
         </nav>
 
         <header className="flex flex-col sm:flex-row gap-6 mb-8 pb-8 border-b border-[#252525]">