feat: tier names + per-tier prices on offer cards, unified admin UI

- offer editor: per-tier name input (mirrors public_name/internal_name)
- offer list cards: show 3-tier services total + manual public price
- shared PageHeader component, full-width layout across all admin pages
- UI-RULES.md design conventions doc

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/admin/catalog/page.tsx

@@ -1,5 +1,6 @@
 import { getAllServices, getCatalogFieldOptions } from "@/lib/admin-queries";
 import { CatalogSearch } from "./CatalogSearch";
+import { PageHeader } from "@/components/admin/PageHeader";
 
 export const revalidate = 0;
 
@@ -10,11 +11,8 @@ export default async function CatalogPage() {
   ]);
 
   return (
-    <div>
-      <div className="flex items-center justify-between mb-6">
-        <h1 className="text-2xl font-bold text-[#1a1a1a]">Catalogo Servizi</h1>
-      </div>
-
+    <div className="space-y-6">
+      <PageHeader title="Catalogo Servizi" />
       <CatalogSearch services={services} options={options} />
     </div>
   );