fix(stammbaum): raise cross-link opacity to 0.7 + add dash-render test (#724)

Review follow-ups:
- Leonie/UX: 0.55 navy on the sand canvas was ~2.6:1, under the WCAG 1.4.11 3:1
  non-text floor for senior readers; 0.7 clears it.
- Sara/QA: add a browser test that actually renders a cross-level link and
  asserts the distinct 2 6 dash, and that a non-cross-link parent edge stays
  solid — the cadence was previously only validated via the structural
  crossLinks array, never where it renders.

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

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

@@ -28,9 +28,11 @@ let { edges, positions, crossLinks = [], isConnectorActive = () => true }: Props
 
 // Dash cadence + opacity for a cross-link, deliberately distinct from the
 // ended-marriage spouse dash (`4 4`) so the two never read alike (WCAG 1.4.1:
-// geometry carries the meaning too, not stroke alone).
+// geometry carries the meaning too, not stroke alone). Opacity stays at 0.7 so
+// the dotted line clears the WCAG 1.4.11 3:1 non-text contrast floor for
+// senior / low-vision readers (a lighter 0.55 fell just under).
 const CROSS_LINK_DASH = '2 6';
-const CROSS_LINK_OPACITY = 0.55;
+const CROSS_LINK_OPACITY = 0.7;
 
 const crossLinkSet = $derived(new SvelteSet(crossLinks.map((c) => `${c.parentId}->${c.childId}`)));
 function isCrossLink(parentId: string, childId: string): boolean {

frontend/src/lib/person/genealogy/StammbaumConnectors.svelte.test.ts

@@ -0,0 +1,82 @@
+import { describe, it, expect, vi } from 'vitest';
+import { render } from 'vitest-browser-svelte';
+import StammbaumConnectors from './StammbaumConnectors.svelte';
+import { NODE_H } from './layout/buildLayout';
+import type { components } from '$lib/generated/api';
+
+type RelationshipDTO = components['schemas']['RelationshipDTO'];
+
+const P = '00000000-0000-0000-0000-0000000000c1';
+const C = '00000000-0000-0000-0000-0000000000c2';
+const H = '00000000-0000-0000-0000-0000000000c3';
+const W = '00000000-0000-0000-0000-0000000000c4';
+
+function parentEdge(parentId: string, childId: string): RelationshipDTO {
+	return {
+		id: `${parentId}>${childId}`,
+		personId: parentId,
+		relatedPersonId: childId,
+		personDisplayName: '',
+		relatedPersonDisplayName: '',
+		relationType: 'PARENT_OF'
+	};
+}
+
+function endedSpouseEdge(a: string, b: string): RelationshipDTO {
+	return {
+		id: `${a}~${b}`,
+		personId: a,
+		relatedPersonId: b,
+		personDisplayName: '',
+		relatedPersonDisplayName: '',
+		relationType: 'SPOUSE_OF',
+		toYear: 1950
+	};
+}
+
+const positions = new Map([
+	[P, { x: 0, y: 0 }],
+	[C, { x: 400, y: NODE_H + 80 }],
+	[H, { x: 0, y: 400 }],
+	[W, { x: 300, y: 400 }]
+]);
+
+const dashesOf = (selector: string) =>
+	Array.from(document.querySelectorAll(selector))
+		.map((el) => el.getAttribute('stroke-dasharray'))
+		.filter((d): d is string => d !== null);
+
+describe('StammbaumConnectors — cross-link cadence (#724)', () => {
+	it('renders a cross-level link with the distinct 2 6 dash, never the 4 4 ended-marriage dash', async () => {
+		render(StammbaumConnectors, {
+			edges: [parentEdge(P, C), endedSpouseEdge(H, W)],
+			positions,
+			crossLinks: [{ parentId: P, childId: C }]
+		});
+
+		await vi.waitFor(() => {
+			const dashes = dashesOf('line');
+			// The cross-link cadence is present …
+			expect(dashes).toContain('2 6');
+			// … the ended-marriage cadence is present …
+			expect(dashes).toContain('4 4');
+			// … and the two are genuinely different cadences (WCAG 1.4.1: not by
+			// stroke alone, but they must not collapse into the same pattern).
+			expect('2 6').not.toBe('4 4');
+		});
+	});
+
+	it('draws a normal parent→child connector solid when it is NOT a cross-link', async () => {
+		render(StammbaumConnectors, {
+			edges: [parentEdge(P, C)],
+			positions,
+			crossLinks: []
+		});
+
+		await vi.waitFor(() => {
+			// No dashed parent lines at all when nothing is a cross-link.
+			expect(dashesOf('line')).not.toContain('2 6');
+			expect(document.querySelectorAll('line').length).toBeGreaterThan(0);
+		});
+	});
+});