Initial commit of Descrybe v2 without local scratch artifacts.

Drop one-shot tmp/axe scripts and agent i18n scratch so the Gitea tree is deployable.

apps/api/internal/catalog/errors.go

@@ -0,0 +1,39 @@
+package catalog
+
+import "errors"
+
+var (
+	ErrSystemImmutable = errors.New("system records cannot be modified or deleted")
+	ErrNotFound        = errors.New("not found")
+)
+
+// clientError is a validation/business message safe to return to API clients.
+type clientError struct {
+	msg string
+}
+
+func (e *clientError) Error() string { return e.msg }
+
+// ClientMsg marks a message as safe to expose in HTTP 4xx responses.
+func ClientMsg(msg string) error {
+	return &clientError{msg: msg}
+}
+
+// ClientError reports whether err is a known client-facing catalog error.
+func ClientError(err error) (msg string, ok bool) {
+	if err == nil {
+		return "", false
+	}
+	var ce *clientError
+	if errors.As(err, &ce) {
+		return ce.msg, true
+	}
+	switch {
+	case errors.Is(err, ErrNotFound):
+		return "not found", true
+	case errors.Is(err, ErrSystemImmutable):
+		return err.Error(), true
+	default:
+		return "", false
+	}
+}