fix: remove stray closing brace in auth.go

backend/middleware/auth.go

@@ -136,9 +136,6 @@ func GenerateDownloadToken(userID int, username, secret, filePath string) (strin
 	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
 	return token.SignedString([]byte(secret))
 }
-
-}
-
 // GenerateEditToken creates a long-lived edit token for OnlyOffice sessions.
 func GenerateEditToken(userID int, username, secret, filePath string) (string, error) {
 	claims := jwt.MapClaims{