feat: add default_language config parameter

internal/ai/ai.go

@@ -99,7 +99,15 @@ func (a *AI) GenerateReply(emailContent string, contextContent map[string]string
 	// First, detect the language
 	lang, err := a.detectLanguage(emailContent)
 	if err != nil {
-		return "", err
+		if a.config.DefaultLanguage != "" {
+			logger.WithFields(logrus.Fields{
+				"error":           err,
+				"defaultLanguage": a.config.DefaultLanguage,
+			}).Warn("Language detection failed, falling back to default language")
+			lang = a.config.DefaultLanguage
+		} else {
+			return "", err
+		}
 	}
 
 	// Build prompts using exposed methods