fix: set_url_seo and record imports refuse a locale the record does not have (WR-18)

A locale given with a URL write overrode the matched one unchecked, so
"xx" created an entry nothing ever reads while the answer reported
success. SetURLSEO (API, MCP, batch set_seo, records import) now requires
one of the record's locales and refuses others with api.locale_unknown.

classes/owner.go

@@ -156,7 +156,15 @@ func (s *Service) SetURLSEO(ctx context.Context, tx *gorm.DB, in URLSEOWrite) (U
 	}
 	if owner.WrittenTo == WrittenToRecord {
 		locale := owner.Locale
-		if l := strings.TrimSpace(in.Locale); l != "" {
+		if l := strings.TrimSpace(in.Locale); l != "" && l != locale {
+			// Another locale must be one the record describes (WR-18): an
+			// entry in any other would never be read by the resolver or the
+			// SEO tab.
+			if _, known := s.recordLocales(ctx, typ.Key, owner.ID)[l]; !known {
+				return URLSEOResult{}, &ProblemsError{Problems: map[string][]models.Problem{
+					"locale": {{Key: "golem15.seo::lang.api.locale_unknown", Params: map[string]string{"locale": l}}},
+				}}
+			}
 			locale = l
 		}
 		owner.Locale = locale