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/wwwroot/css/admin.css

@@ -1391,6 +1391,23 @@ textarea:focus-visible {
 
 #blazor-loading.show {
   display: flex;
+  animation: overlayFadeIn 0.15s ease-out;
+}
+
+@keyframes overlayFadeIn {
+  from { opacity: 0; }
+  to   { opacity: 1; }
+}
+
+/* Page content fade-in on each route mount */
+.admin-page-hero,
+.admin-login-page {
+  animation: adminPageIn 0.25s ease-out;
+}
+
+@keyframes adminPageIn {
+  from { opacity: 0; transform: translateY(6px); }
+  to   { opacity: 1; transform: translateY(0); }
 }
 
 .blazor-loading-overlay {