feat: 시즌별 마케팅 + 공지사항 관리 기능 추가

- 연간 세무 캘린더(7개 시즌) 기반 자동 Hero 섹션 전환
- 시즌 감지 시 D-Day 카운트다운, 긴박감 배지, 시즌 CTA 표시
- 서비스 카드 순서 시즌 관련 항목 우선 정렬
- 어드민 공지사항 CRUD (등록·수정·삭제, 기간·유형 설정)
- 홈페이지 상단 공지 배너 자동 노출 (일반/배너/긴급)
- CLAUDE.md에 세무 캘린더 및 마케팅 방향 하네스 추가

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

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

@@ -1,24 +1,60 @@
 @inherits LayoutComponentBase
 
-<MudLayout>
-    <MudAppBar Elevation="1">
-        <MudText Typo="Typo.h6" Class="ml-3">백원숙 세무회계 관리자</MudText>
+<MudLayout Class="admin-shell">
+    <MudAppBar Elevation="0" Class="admin-topbar">
+        <MudIconButton Icon="@Icons.Material.Filled.Menu"
+                       Color="Color.Inherit"
+                       Edge="Edge.Start"
+                       Class="admin-menu-button"
+                       OnClick="@ToggleDrawer" />
+        <div class="admin-topbar-title">
+            <MudText Typo="Typo.caption">TaxBaik Backoffice</MudText>
+            <MudText Typo="Typo.h6">백원숙 세무회계 관리자</MudText>
+        </div>
         <MudSpacer />
-        <MudButton Color="Color.Inherit" Href="/taxbaik">공개 사이트</MudButton>
-        <MudButton Href="/taxbaik/admin/logout">로그아웃</MudButton>
+        <MudButton Class="admin-topbar-action"
+                   Variant="Variant.Outlined"
+                   Color="Color.Inherit"
+                   StartIcon="@Icons.Material.Filled.OpenInNew"
+                   Href="/taxbaik">
+            공개 사이트
+        </MudButton>
+        <MudButton Class="admin-topbar-action"
+                   Variant="Variant.Filled"
+                   Color="Color.Primary"
+                   StartIcon="@Icons.Material.Filled.Logout"
+                   Href="/taxbaik/admin/logout">
+            로그아웃
+        </MudButton>
     </MudAppBar>
 
-    <MudDrawer @bind-open="@drawerOpen" Elevation="1" Variant="DrawerVariant.Responsive" Breakpoint="Breakpoint.Md">
-        <MudNavMenu>
-            <MudNavLink Href="/taxbaik/admin/dashboard" 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>
+    <MudDrawer @bind-open="@drawerOpen"
+               Elevation="0"
+               Variant="DrawerVariant.Responsive"
+               Breakpoint="Breakpoint.Md"
+               Class="admin-drawer">
+        <div class="admin-drawer-brand">
+            <div class="admin-brand-mark">T</div>
+            <div>
+                <MudText Typo="Typo.subtitle1">TaxBaik</MudText>
+                <MudText Typo="Typo.caption">세무 운영 콘솔</MudText>
+            </div>
+        </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>
+            <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>
+        <div class="admin-drawer-footer">
+            <MudText Typo="Typo.caption">운영 기준</MudText>
+            <MudText Typo="Typo.body2">변경 사항은 배포 후 Playwright로 검증합니다.</MudText>
+        </div>
     </MudDrawer>
 
-    <MudMainContent>
-        <MudContainer MaxWidth="MaxWidth.Large" Class="my-4 px-3 px-md-0">
+    <MudMainContent Class="admin-main">
+        <MudContainer MaxWidth="MaxWidth.False" Class="admin-content">
             @Body
         </MudContainer>
     </MudMainContent>
@@ -26,4 +62,9 @@
 
 @code {
     private bool drawerOpen = true;
+
+    private void ToggleDrawer()
+    {
+        drawerOpen = !drawerOpen;
+    }
 }