수정: 빌드 오류 해결 (PageModel 네임스페이스, Blazor 문법, 응답 압축)

- @model 선언에 정확한 네임스페이스 지정
- Snackbar 호출 수정 (MudBlazor 6.x 호환)
- GzipCompressionProvider import 추가
- Dashboard Color.TextSecondary 제거
- Admin App.razor MUI CSS 제거

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

TaxBaik.Application/TaxBaik.Application.csproj

@@ -2,6 +2,11 @@
   <ItemGroup>
     <ProjectReference Include="..\TaxBaik.Domain\TaxBaik.Domain.csproj" />
   </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="8.0.0" />
+  </ItemGroup>
+
   <PropertyGroup>
     <TargetFramework>net8.0</TargetFramework>
     <Nullable>enable</Nullable>