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/messages/de.json

@@ -960,6 +960,8 @@
 	"relation_error_duplicate": "Diese Beziehung gibt es bereits.",
 	"relation_error_circular": "Diese Beziehung würde einen Kreis erzeugen.",
 	"relation_error_self": "Eine Person kann nicht mit sich selbst verbunden werden.",
+	"relation_year_from": "ab {year}",
+	"relation_year_to": "bis {year}",
 	"relation_year_error_bis_before_von": "Bis-Jahr darf nicht vor Von-Jahr liegen.",
 	"relation_label_family_member": "Als Familienmitglied",
 	"relation_label_in_tree": "Erscheint im Stammbaum",

frontend/messages/en.json

@@ -960,6 +960,8 @@
 	"relation_error_duplicate": "This relationship already exists.",
 	"relation_error_circular": "This relationship would form a cycle.",
 	"relation_error_self": "A person cannot be related to themselves.",
+	"relation_year_from": "from {year}",
+	"relation_year_to": "until {year}",
 	"relation_year_error_bis_before_von": "End year must not precede start year.",
 	"relation_label_family_member": "Family member",
 	"relation_label_in_tree": "Appears in the family tree",

frontend/messages/es.json

@@ -960,6 +960,8 @@
 	"relation_error_duplicate": "Esta relación ya existe.",
 	"relation_error_circular": "Esta relación crearía un ciclo.",
 	"relation_error_self": "Una persona no puede estar relacionada consigo misma.",
+	"relation_year_from": "desde {year}",
+	"relation_year_to": "hasta {year}",
 	"relation_year_error_bis_before_von": "El año final no puede ser anterior al año inicial.",
 	"relation_label_family_member": "Miembro de la familia",
 	"relation_label_in_tree": "Aparece en el árbol genealógico",

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 '';
 }