feat: revamp UI/UX of homepage & portal, clean warnings, and update ROADMAP_WBS

TaxBaik.Web/Services/CustomAuthenticationStateProvider.cs

@@ -79,7 +79,7 @@ public class CustomAuthenticationStateProvider : AuthenticationStateProvider
                 }
             }
 
-            var principal = _authService.ValidateToken(accessToken);
+            var principal = _authService.ValidateToken(accessToken ?? string.Empty);
             if (principal == null)
             {
                 await LogoutAsync();
@@ -115,13 +115,13 @@ public class CustomAuthenticationStateProvider : AuthenticationStateProvider
     private bool ShouldRefreshToken()
     {
         // 토큰이 5분 이내로 만료되면 갱신 (300초 = 5분)
-        if (_tokenStore.TokenExpiryTicks <= 0)
+        if (!_tokenStore.TokenExpiryTicks.HasValue || _tokenStore.TokenExpiryTicks.Value <= 0)
             return false;
 
         const int refreshThresholdSeconds = 300;
         try
         {
-            var expiryTime = new DateTime((long)_tokenStore.TokenExpiryTicks, DateTimeKind.Utc);
+            var expiryTime = new DateTime(_tokenStore.TokenExpiryTicks.Value, DateTimeKind.Utc);
             var timeUntilExpiry = expiryTime - DateTime.UtcNow;
             return timeUntilExpiry.TotalSeconds <= refreshThresholdSeconds && timeUntilExpiry.TotalSeconds > 0;
         }