ux: eliminate white-flash on Blazor navigation from Inquiry page

- App.razor: loading overlay starts with `show` class (visible on cold load)
- admin-session.js: add showLoading()/hideLoading(); MutationObserver detects
  .admin-page-hero / .admin-login-page instead of mud-element count threshold;
  observer restarts on every navigation cycle via LocationChanged
- MainLayout.razor: subscribe to NavigationManager.LocationChanged →
  call JS showLoading() on every route change; implements IDisposable
- InquiryList.razor: remove unused IInquiryRepository injection; load data
  once (GetPagedAsync(1,200)) and pass IReadOnlyList to all six tab panels
- InquiryTable.razor: accept Inquiries parameter; filter synchronously in
  OnParametersSet() — eliminates 6 redundant API calls per page visit
- admin.css: overlay fade-in animation (0.15s); page content fade-in on
  route mount via .admin-page-hero / .admin-login-page animation (0.25s)

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

TaxBaik.Web/Components/Admin/App.razor

@@ -24,7 +24,7 @@
             <span>배포 또는 서버 재시작 중이면 잠시 후 자동으로 새로고침됩니다.</span>
         </div>
     </div>
-    <div id="blazor-loading" class="blazor-loading-overlay">
+    <div id="blazor-loading" class="blazor-loading-overlay show">
         <div class="blazor-loading-spinner">
             <div class="spinner"></div>
             <p>로드 중...</p>

TaxBaik.Web/Components/Admin/InquiryTable.razor

@@ -1,6 +1,3 @@
-@using TaxBaik.Web.Services
-@inject IInquiryBrowserClient InquiryClient
-
 <MudSimpleTable Striped="true" Dense="true" Class="admin-table mt-4">
     <thead>
         <tr>
@@ -37,24 +34,19 @@
 </MudSimpleTable>
 
 @code {
+    [Parameter, EditorRequired]
+    public IReadOnlyList<Domain.Entities.Inquiry> Inquiries { get; set; } = [];
+
     [Parameter]
     public string Status { get; set; } = "";
 
-    private List<Domain.Entities.Inquiry> inquiries = [];
-    private List<Domain.Entities.Inquiry> filteredInquiries = [];
+    private IReadOnlyList<Domain.Entities.Inquiry> filteredInquiries = [];
 
-    protected override async Task OnInitializedAsync()
-    {
-        var (items, _) = await InquiryClient.GetPagedAsync(1, 100);
-        inquiries = items.ToList();
-        FilterInquiries();
-    }
-
-    private void FilterInquiries()
+    protected override void OnParametersSet()
     {
         filteredInquiries = string.IsNullOrEmpty(Status)
-            ? inquiries
-            : inquiries.Where(x => x.Status == Status).ToList();
+            ? Inquiries
+            : Inquiries.Where(x => x.Status == Status).ToList();
     }
 
     private static string GetPreview(string message)
@@ -77,9 +69,4 @@
     };
 
     private static string GetStatusLabel(string status) => InquiryStatusMapper.Labels.GetValueOrDefault(status, status);
-
-    protected override async Task OnParametersSetAsync()
-    {
-        FilterInquiries();
-    }
 }

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

@@ -1,4 +1,7 @@
 @inherits LayoutComponentBase
+@inject NavigationManager Navigation
+@inject IJSRuntime JS
+@implements IDisposable
 
 <MudLayout Class="admin-shell">
     <MudAppBar Elevation="0" Class="admin-topbar">
@@ -73,8 +76,23 @@
     private bool expandedCustomerGroup = true;
     private bool expandedWebsiteGroup = false;
 
+    protected override void OnInitialized()
+    {
+        Navigation.LocationChanged += OnLocationChanged;
+    }
+
+    private void OnLocationChanged(object? sender, LocationChangedEventArgs args)
+    {
+        _ = InvokeAsync(() => JS.InvokeVoidAsync("taxbaikAdminSession.showLoading"));
+    }
+
     private void ToggleDrawer()
     {
         drawerOpen = !drawerOpen;
     }
+
+    public void Dispose()
+    {
+        Navigation.LocationChanged -= OnLocationChanged;
+    }
 }

TaxBaik.Web/Components/Admin/Pages/Inquiries/InquiryList.razor

@@ -1,7 +1,7 @@
 @page "/admin/inquiries"
 @attribute [Authorize]
-@using TaxBaik.Domain.Interfaces
-@inject IInquiryRepository InquiryRepository
+@using TaxBaik.Web.Services
+@inject IInquiryBrowserClient InquiryClient
 
 <PageTitle>문의 관리</PageTitle>
 
@@ -13,25 +13,44 @@
     </div>
 </section>
 
-<MudPaper Class="admin-surface" Elevation="0">
-<MudTabs Rounded="true" Elevation="0" Class="admin-tabs">
-    <MudTabPanel Text="전체">
-        <InquiryTable Status="" />
-    </MudTabPanel>
-    <MudTabPanel Text="신규">
-        <InquiryTable Status="new" />
-    </MudTabPanel>
-    <MudTabPanel Text="상담중">
-        <InquiryTable Status="consulting" />
-    </MudTabPanel>
-    <MudTabPanel Text="계약완료">
-        <InquiryTable Status="contracted" />
-    </MudTabPanel>
-    <MudTabPanel Text="거절">
-        <InquiryTable Status="rejected" />
-    </MudTabPanel>
-    <MudTabPanel Text="종결">
-        <InquiryTable Status="closed" />
-    </MudTabPanel>
-</MudTabs>
-</MudPaper>
+@if (isLoading)
+{
+    <MudProgressCircular Indeterminate="true" Class="ma-4" />
+}
+else
+{
+    <MudPaper Class="admin-surface" Elevation="0">
+    <MudTabs Rounded="true" Elevation="0" Class="admin-tabs">
+        <MudTabPanel Text="전체">
+            <InquiryTable Inquiries="allInquiries" Status="" />
+        </MudTabPanel>
+        <MudTabPanel Text="신규">
+            <InquiryTable Inquiries="allInquiries" Status="new" />
+        </MudTabPanel>
+        <MudTabPanel Text="상담중">
+            <InquiryTable Inquiries="allInquiries" Status="consulting" />
+        </MudTabPanel>
+        <MudTabPanel Text="계약완료">
+            <InquiryTable Inquiries="allInquiries" Status="contracted" />
+        </MudTabPanel>
+        <MudTabPanel Text="거절">
+            <InquiryTable Inquiries="allInquiries" Status="rejected" />
+        </MudTabPanel>
+        <MudTabPanel Text="종결">
+            <InquiryTable Inquiries="allInquiries" Status="closed" />
+        </MudTabPanel>
+    </MudTabs>
+    </MudPaper>
+}
+
+@code {
+    private bool isLoading = true;
+    private IReadOnlyList<Domain.Entities.Inquiry> allInquiries = [];
+
+    protected override async Task OnInitializedAsync()
+    {
+        var (items, _) = await InquiryClient.GetPagedAsync(1, 200);
+        allInquiries = items.ToList();
+        isLoading = false;
+    }
+}