fix: enhance error handling for Gemini API key validation

Author: songquanpeng

monitor/manage.go

@@ -35,6 +35,8 @@ func ShouldDisableChannel(err *model.Error, statusCode int) bool {
 		strings.Contains(lowerMessage, "balance") ||
 		strings.Contains(lowerMessage, "permission denied") ||
 		strings.Contains(lowerMessage, "organization has been restricted") || // groq
+		strings.Contains(lowerMessage, "api key not valid") || // gemini
+		strings.Contains(lowerMessage, "api key expired") || // gemini
 		strings.Contains(lowerMessage, "已欠费") {
 		return true
 	}