fix: logout, accordion, and drawer interactivity issues

**Issues Fixed:**

1. ✅ Logout not working
   - Created Logout.razor page (was missing)
   - Properly calls AuthStateProvider.LogoutAsync()
   - Redirects to login page with forceLoad: true
   - Button click now triggers async logout flow

2. ✅ Accordion state not persisting
   - Changed MudNavGroup from fixed Expanded=true/false
   - to @bind-Expanded data binding
   - Now properly toggles between expanded/collapsed
   - State persists across clicks
   - Added expandedCustomerGroup, expandedWebsiteGroup properties

3. ✅ Drawer responsiveness
   - Already working with @bind-open="@drawerOpen"
   - ToggleDrawer() properly toggles state
   - Responsive behavior controlled via Breakpoint.Md

**Implementation:**
- Logout.razor: New page for async logout
  - Calls AuthStateProvider.LogoutAsync()
  - Clears TokenStore + localStorage
  - Redirects to /admin/login

- MainLayout.razor: Accordion interactivity
  - @bind-Expanded replaces hardcoded Expanded properties
  - Each group has independent state variable
  - Click properly toggles group expansion

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

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

@@ -42,11 +42,11 @@
         </div>
         <MudNavMenu Class="admin-nav">
             <MudNavLink Href="/taxbaik/admin/dashboard" Match="NavLinkMatch.All" Icon="@Icons.Material.Filled.Dashboard">대시보드</MudNavLink>
-            <MudNavGroup Title="고객 관리" Icon="@Icons.Material.Filled.PeopleAlt" Expanded="true">
+            <MudNavGroup Title="고객 관리" Icon="@Icons.Material.Filled.PeopleAlt" @bind-Expanded="@expandedCustomerGroup">
                 <MudNavLink Href="/taxbaik/admin/clients" Icon="@Icons.Material.Filled.ContactPage">고객 카드</MudNavLink>
                 <MudNavLink Href="/taxbaik/admin/tax-filings" Icon="@Icons.Material.Filled.CalendarMonth">신고 일정</MudNavLink>
             </MudNavGroup>
-            <MudNavGroup Title="홈페이지" Icon="@Icons.Material.Filled.Home" Expanded="false">
+            <MudNavGroup Title="홈페이지" Icon="@Icons.Material.Filled.Home" @bind-Expanded="@expandedWebsiteGroup">
                 <MudNavLink Href="/taxbaik/admin/announcements" Icon="@Icons.Material.Filled.Campaign">공지사항</MudNavLink>
                 <MudNavLink Href="/taxbaik/admin/faqs" Icon="@Icons.Material.Filled.QuestionAnswer">FAQ 관리</MudNavLink>
                 <MudNavLink Href="/taxbaik/admin/blog" Icon="@Icons.Material.Filled.Article">블로그 관리</MudNavLink>
@@ -70,6 +70,8 @@
 
 @code {
     private bool drawerOpen = true;
+    private bool expandedCustomerGroup = true;
+    private bool expandedWebsiteGroup = false;
 
     private void ToggleDrawer()
     {

TaxBaik.Web/Components/Admin/Pages/Logout.razor

@@ -0,0 +1,17 @@
+@page "/admin/logout"
+@using TaxBaik.Web.Services
+@inject CustomAuthenticationStateProvider AuthStateProvider
+@inject NavigationManager NavigationManager
+
+<PageTitle>로그아웃</PageTitle>
+
+@code {
+    protected override async Task OnInitializedAsync()
+    {
+        // 사용자 로그아웃
+        await AuthStateProvider.LogoutAsync();
+
+        // 로그인 페이지로 리다이렉트
+        NavigationManager.NavigateTo("/taxbaik/admin/login", forceLoad: true);
+    }
+}