feat: WBS-CRM-01 고객 카드 (Client Card) Phase 1 구현

DB:
- V006__CreateClients.sql: clients 테이블 (name, company_name, phone,
  email, service_type, tax_type, status, source, memo)

Domain:
- Client 엔티티
- IClientRepository (GetPagedAsync 이름/연락처/회사명 검색 + 상태 필터)

Infrastructure:
- ClientRepository: ILIKE 검색, 페이징, CRUD

Application:
- ClientService: ServiceTypes/TaxTypes/Sources 상수 정의
- CreateClientDto

Admin UI:
- ClientList.razor: 검색바 + 상태 필터 + 페이징 테이블
- ClientEdit.razor: 기본정보/세무정보/관리정보 섹션 폼
- MainLayout: 고객 관리 NavGroup 추가, 홈페이지 메뉴 그룹화

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

TaxBaik.Web/Components/Admin/Layout/MainLayout.razor

@@ -42,8 +42,13 @@
         </div>
         <MudNavMenu Class="admin-nav">
             <MudNavLink Href="/taxbaik/admin/dashboard" Match="NavLinkMatch.All" Icon="@Icons.Material.Filled.Dashboard">대시보드</MudNavLink>
-            <MudNavLink Href="/taxbaik/admin/announcements" Icon="@Icons.Material.Filled.Campaign">공지사항</MudNavLink>
-            <MudNavLink Href="/taxbaik/admin/blog" Icon="@Icons.Material.Filled.Article">블로그 관리</MudNavLink>
+            <MudNavGroup Title="고객 관리" Icon="@Icons.Material.Filled.PeopleAlt" Expanded="true">
+                <MudNavLink Href="/taxbaik/admin/clients" Icon="@Icons.Material.Filled.ContactPage">고객 카드</MudNavLink>
+            </MudNavGroup>
+            <MudNavGroup Title="홈페이지" Icon="@Icons.Material.Filled.Home" Expanded="false">
+                <MudNavLink Href="/taxbaik/admin/announcements" Icon="@Icons.Material.Filled.Campaign">공지사항</MudNavLink>
+                <MudNavLink Href="/taxbaik/admin/blog" Icon="@Icons.Material.Filled.Article">블로그 관리</MudNavLink>
+            </MudNavGroup>
             <MudNavLink Href="/taxbaik/admin/inquiries" Icon="@Icons.Material.Filled.Forum">문의 관리</MudNavLink>
             <MudNavLink Href="/taxbaik/admin/settings" Icon="@Icons.Material.Filled.Tune">설정</MudNavLink>
         </MudNavMenu>