Fix intermittent login loop caused by timezone and race condition bugs

- Fix DateTime parsing to preserve UTC timezone from ISO 8601 'Z' suffix
  using DateTimeOffset.TryParse with DateTimeStyles.RoundtripKind
  (TokenStorageService.cs, GitHubCallback.razor)
- Remove forceLoad: true from Login.razor to prevent race condition
- Fix _isInitialized one-shot failure in LrmAuthStateProvider - only
  mark as initialized if user fetch succeeds, allowing retry on failure

Author: nickprotop

cloud/src/LrmCloud.Web/Pages/Auth/GitHubCallback.razor

@@ -1,5 +1,6 @@
 @page "/auth/github/callback"
 @layout AuthLayout
+@using System.Globalization
 @inject AuthService AuthService
 @inject NavigationManager Navigation
 @inject IJSRuntime JS
@@ -62,21 +63,21 @@
                 return;
             }
 
-            // Parse dates
-            if (!DateTime.TryParse(Uri.UnescapeDataString(expiresAtStr), out var expiresAt) ||
-                !DateTime.TryParse(Uri.UnescapeDataString(refreshTokenExpiresAtStr), out var refreshTokenExpiresAt))
+            // Parse dates - use RoundtripKind to preserve UTC timezone from ISO 8601 "Z" suffix
+            if (!DateTimeOffset.TryParse(Uri.UnescapeDataString(expiresAtStr), null, DateTimeStyles.RoundtripKind, out var expiresAtOffset) ||
+                !DateTimeOffset.TryParse(Uri.UnescapeDataString(refreshTokenExpiresAtStr), null, DateTimeStyles.RoundtripKind, out var refreshTokenExpiresAtOffset))
             {
                 _errorMessage = "Invalid token expiration data. Please try again.";
                 StateHasChanged();
                 return;
             }
 
-            // Process the tokens
+            // Process the tokens (convert to UTC DateTime)
             var result = await AuthService.ProcessGitHubCallbackAsync(
                 Uri.UnescapeDataString(token),
-                expiresAt,
+                expiresAtOffset.UtcDateTime,
                 Uri.UnescapeDataString(refreshToken),
-                refreshTokenExpiresAt);
+                refreshTokenExpiresAtOffset.UtcDateTime);
 
             if (result.IsSuccess)
             {

cloud/src/LrmCloud.Web/Pages/Auth/Login.razor

@@ -103,7 +103,8 @@
 
             if (result.IsSuccess)
             {
-                Navigation.NavigateTo(ReturnUrl ?? "", forceLoad: true);
+                // Don't use forceLoad: true - causes race condition with localStorage persistence
+                Navigation.NavigateTo(ReturnUrl ?? "");
             }
             else
             {

cloud/src/LrmCloud.Web/Services/LrmAuthStateProvider.cs

@@ -71,8 +71,9 @@ public override async Task<AuthenticationState> GetAuthenticationStateAsync()
         // Try to get user info from cache or fetch from API
         if (_cachedUser == null && !_isInitialized)
         {
-            _isInitialized = true;
             _cachedUser = await FetchCurrentUserAsync();
+            // Only mark as initialized if fetch succeeded - allows retry on failure
+            _isInitialized = _cachedUser != null;
         }
 
         if (_cachedUser == null)

cloud/src/LrmCloud.Web/Services/TokenStorageService.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using Blazored.LocalStorage;
 
 namespace LrmCloud.Web.Services;
@@ -41,14 +42,20 @@ public async Task StoreTokensAsync(string accessToken, string refreshToken, Date
     {
         var expiry = await _localStorage.GetItemAsStringAsync(TokenExpiryKey);
         if (string.IsNullOrEmpty(expiry)) return null;
-        return DateTime.TryParse(expiry, out var dt) ? dt : null;
+        // Use RoundtripKind to preserve UTC timezone from ISO 8601 "Z" suffix
+        return DateTimeOffset.TryParse(expiry, null, DateTimeStyles.RoundtripKind, out var dt)
+            ? dt.UtcDateTime
+            : null;
     }
 
     public async Task<DateTime?> GetRefreshExpiryAsync()
     {
         var expiry = await _localStorage.GetItemAsStringAsync(RefreshExpiryKey);
         if (string.IsNullOrEmpty(expiry)) return null;
-        return DateTime.TryParse(expiry, out var dt) ? dt : null;
+        // Use RoundtripKind to preserve UTC timezone from ISO 8601 "Z" suffix
+        return DateTimeOffset.TryParse(expiry, null, DateTimeStyles.RoundtripKind, out var dt)
+            ? dt.UtcDateTime
+            : null;
     }
 
     public async Task<bool> IsTokenExpiredAsync()