fix(stammbaum): i18n for year-range labels in StammbaumCard

Replaces hardcoded German strings "ab {from}" / "bis {to}" in yearRange()
with parameterized Paraglide keys relation_year_from / relation_year_to,
added to all three message files (de/en/es).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/StammbaumCard.svelte

@@ -109,8 +109,8 @@ function yearRange(rel: RelationshipDTO): string {
 	const from = rel.fromYear;
 	const to = rel.toYear;
 	if (from && to) return `${from}–${to}`;
-	if (from) return `ab ${from}`;
-	if (to) return `bis ${to}`;
+	if (from) return m.relation_year_from({ year: from });
+	if (to) return m.relation_year_to({ year: to });
 	return '';
 }