feat(auth): fix post-login redirection ArgumentException and introduce premium client-side hydration preloader

src/NexusReader.UI.Shared/Layout/MainHubLayout.razor

@@ -4,6 +4,14 @@
 @using NexusReader.Application.Abstractions.Services
 @using NexusReader.UI.Shared.Services
 
+@if (!_isFullyLoaded)
+{
+    <div class="app-preloader" style="backdrop-filter: blur(15px); background: rgba(18, 18, 18, 0.95); z-index: 100000;">
+        <div class="preloader-spinner"></div>
+        <div class="preloader-text">Synchronizing Secure Session...</div>
+    </div>
+}
+
 <div class="hub-container @(_isMobileMenuOpen ? "mobile-menu-open" : "")">
     <AuthorizeView>
         <Authorized>
@@ -80,6 +88,7 @@
                         </div>
                         <span class="nav-text">Concenters</span>
                     </NavLink>
+
                 </nav>
 
                 <div class="sidebar-footer">
@@ -113,6 +122,7 @@
 
     private bool _isSyncing = false;
     private bool _isMobileMenuOpen = false;
+    private bool _isFullyLoaded = false;
 
     protected override async Task OnInitializedAsync()
     {
@@ -127,6 +137,15 @@
         }
     }
 
+    protected override void OnAfterRender(bool firstRender)
+    {
+        if (firstRender)
+        {
+            _isFullyLoaded = true;
+            StateHasChanged();
+        }
+    }
+
     private void ToggleMobileMenu()
     {
         _isMobileMenuOpen = !_isMobileMenuOpen;