Refactor admin dashboard and standardize UI shells

src/TaxBaik.Web.Client/Components/Admin/Pages/Dashboard.razor

@@ -1,14 +1,5 @@
 @page "/admin/dashboard"
 @rendermode @(new InteractiveWebAssemblyRenderMode(prerender: false))
+@attribute [Authorize]
 
-<PageTitle>대시보드</PageTitle>
-
-<section style="padding: 24px;">
-    <h1 style="margin: 0 0 12px 0; font-size: 1.8rem;">대시보드</h1>
-    <p style="margin: 0 0 12px 0;">관리자 SPA 부팅 검증용 최소 화면입니다.</p>
-    <ul>
-        <li>WASM 부팅 성공 여부</li>
-        <li>라우팅 성공 여부</li>
-        <li>JS interop 예외 여부</li>
-    </ul>
-</section>
+<DashboardOverview />