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/page.tsx

@@ -12,6 +12,7 @@ import { getRevenueForecast12Months, getOffersSoldBreakdown } from "@/lib/foreca
 import { YearSelector, MonthlyChart } from "@/components/admin/YearSelector";
 import { ForecastChart } from "@/components/admin/ForecastChart";
 import { OffersSoldChart } from "@/components/admin/OffersSoldChart";
+import { PageHeader } from "@/components/admin/PageHeader";
 
 export const revalidate = 0;
 
@@ -95,8 +96,8 @@ export default async function AdminDashboard({
   const maxClientSeconds = timeByClient[0]?.totalSeconds ?? 1;
 
   return (
-    <div className="max-w-5xl">
-      <h1 className="text-2xl font-bold text-gray-900 mb-6">Dashboard</h1>
+    <div className="space-y-6">
+      <PageHeader title="Dashboard" />
 
       {/* Follow-up Widget */}
       <div className="mb-8">