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/leads/page.tsx

@@ -1,6 +1,7 @@
 import { getLeadsWithTags, getLeadFieldOptions } from "@/lib/admin-queries";
 import { LeadsViewToggle } from "@/components/admin/leads/LeadsViewToggle";
 import { CreateLeadModal } from "@/components/admin/leads/LeadForm";
+import { PageHeader } from "@/components/admin/PageHeader";
 
 export const revalidate = 0;
 
@@ -12,11 +13,7 @@ export default async function LeadsPage() {
 
   return (
     <div className="space-y-6">
-      <div className="flex justify-between items-center">
-        <h1 className="text-2xl font-bold text-[#1a1a1a]">Lead Pipeline</h1>
-        <CreateLeadModal />
-      </div>
-
+      <PageHeader title="Lead Pipeline" action={<CreateLeadModal />} />
       <LeadsViewToggle leads={leads} options={options} />
     </div>
   );