Refactor admin dashboard and standardize UI shells

src/TaxBaik.Web.Client/Components/Admin/Pages/Clients/ClientDetail.razor

@@ -11,13 +11,7 @@
 
 <PageTitle>고객 상세</PageTitle>
 
-<section class="admin-page-hero">
-    <div>
-        <MudText Typo="Typo.caption" Class="admin-eyebrow">Client Details</MudText>
-        <MudText Typo="Typo.h4" Class="admin-page-title">고객 상세</MudText>
-        <MudText Typo="Typo.body2" Class="admin-page-subtitle">고객 정보와 상담 이력을 관리합니다.</MudText>
-    </div>
-</section>
+<AdminPageHeader Title="고객 상세" Eyebrow="Client Details" Subtitle="고객 정보와 상담 이력을 관리합니다." />
 
 @if (client == null)
 {