feat(stammbaum): render cross-level links with a distinct dash (#724)

StammbaumConnectors takes the layout's crossLinks and draws those parent->child
connectors with a 2 6 dash at reduced opacity — deliberately distinct from the
ended-marriage spouse dash (4 4) and from a solid parent drop. Geometry still
lands on the child top, so the meaning is carried redundantly (WCAG 1.4.1).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/person/genealogy/StammbaumTree.svelte

@@ -334,6 +334,7 @@ function handleCanvasKey(event: KeyboardEvent) {
 		<StammbaumConnectors
 			edges={edges}
 			positions={layout.positions}
+			crossLinks={layout.crossLinks}
 			isConnectorActive={isConnectorActive}
 		/>