feat: support time_zone for user registration context

gateway/internal/restapi/public_auth.go

@@ -79,6 +79,11 @@ type ConfirmEmailCodeInput struct {
 	// ClientPublicKey is the standard base64-encoded raw 32-byte Ed25519 public
 	// key that should be registered for the created device session.
 	ClientPublicKey string `json:"client_public_key"`
+
+	// TimeZone is the client-selected IANA time zone name forwarded to the
+	// Auth / Session Service as registration context for first-time user
+	// creation.
+	TimeZone string `json:"time_zone"`
 }
 
 // ConfirmEmailCodeResult describes the public REST and adapter payload
@@ -391,6 +396,11 @@ func validateConfirmEmailCodeInput(input *ConfirmEmailCodeInput) error {
 		return errors.New("client_public_key must not be empty")
 	}
 
+	input.TimeZone = strings.TrimSpace(input.TimeZone)
+	if input.TimeZone == "" {
+		return errors.New("time_zone must not be empty")
+	}
+
 	return nil
 }