fix(stammbaum): state-aware aria-label on family-member toggle — WCAG accessible name

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

frontend/src/lib/components/StammbaumCard.svelte

@@ -76,6 +76,9 @@ function yearRange(rel: RelationshipDTO): string {
 					type="submit"
 					role="switch"
 					aria-checked={familyMember}
+					aria-label={familyMember
+						? m.relation_toggle_remove_from_tree()
+						: m.relation_toggle_add_to_tree()}
 					class="inline-flex items-center gap-2 font-sans text-xs font-medium text-ink-2 transition-colors hover:text-ink"
 				>
 					<span