refactor: Web과 Admin 통합 - 단일 포트 5001로 운영

분리의 단점을 제거하고 단일 앱으로 통합:

구조 변경:
- TaxBaik.Admin → TaxBaik.Web/Components/Admin/
- Admin Services → TaxBaik.Web/Services/
- 포트: 5001 (기존 5002 제거)

경로:
- 홈페이지: http://localhost:5001/taxbaik
- 관리자: http://localhost:5001/taxbaik/admin

기술:
- Razor Pages (Web) + Blazor Server (Admin) 통합
- 단일 Program.cs로 양쪽 모두 지원
- JWT 인증 유지
- MudBlazor UI 유지

장점:
- 개발 복잡도 감소 (터미널 1개)
- 배포 단순화 (앱 1개)
- DB 마이그레이션 1회 실행

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

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

@@ -0,0 +1,41 @@
+@using Microsoft.AspNetCore.Components.Authorization
+@inherits LayoutComponentBase
+
+<AuthorizeView>
+    <Authorized>
+        <MudThemeProvider />
+        <MudDialogProvider />
+        <MudSnackbarProvider />
+
+        <MudLayout>
+            <MudAppBar Elevation="1">
+                <MudText Typo="Typo.h6" Class="ml-3">백원숙 세무회계 관리자</MudText>
+                <MudSpacer />
+                <MudButton Color="Color.Inherit" Href="/taxbaik">공개 사이트</MudButton>
+                <MudButton Href="/taxbaik/admin/logout">로그아웃</MudButton>
+            </MudAppBar>
+
+            <MudDrawer @bind-open="@drawerOpen" Elevation="1">
+                <MudNavMenu>
+                    <MudNavLink Href="/taxbaik/admin/" Match="NavLinkMatch.All">📊 대시보드</MudNavLink>
+                    <MudNavLink Href="/taxbaik/admin/blog">📝 블로그 관리</MudNavLink>
+                    <MudNavLink Href="/taxbaik/admin/inquiries">💬 문의 관리</MudNavLink>
+                    <MudNavLink Href="/taxbaik/admin/settings">⚙️ 설정</MudNavLink>
+                </MudNavMenu>
+            </MudDrawer>
+
+            <MudMainContent>
+                <MudContainer MaxWidth="MaxWidth.Large" Class="my-4">
+                    @Body
+                </MudContainer>
+            </MudMainContent>
+        </MudLayout>
+    </Authorized>
+    <NotAuthorized>
+        @Body
+    </NotAuthorized>
+</AuthorizeView>
+
+@code {
+    private bool drawerOpen = true;
+}