fix: remove unnecessary OAuth warning when API key auth is present

API key authentication is a valid authentication method. The warning
suggesting users run 'kernel login' for OAuth was confusing and
unnecessary when they already have working API key authentication.

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

Author: rgarcia

cmd/auth.go

@@ -88,7 +88,6 @@ func runAuth(cmd *cobra.Command, args []string) error {
 			} else {
 				pterm.Info.Printf("API Key: %s\n", strings.Repeat("*", len(apiKey)))
 			}
-			pterm.Warning.Println("Consider running 'kernel login' to use OAuth authentication")
 			return nil
 		}