feat: add audit log with email notification (#26)

backend/internal/model/app_config.go

@@ -13,4 +13,11 @@ type AppConfig struct {
 	BackgroundImageType AppConfigVariable
 	LogoImageType       AppConfigVariable
 	SessionDuration     AppConfigVariable
+
+	EmailEnabled AppConfigVariable
+	SmtpHost     AppConfigVariable
+	SmtpPort     AppConfigVariable
+	SmtpFrom     AppConfigVariable
+	SmtpUser     AppConfigVariable
+	SmtpPassword AppConfigVariable
 }