test(stammbaum): assert r=6 marriage dot fill is var(--c-primary) (#361)

Cycle-2 follow-up from Sara. The radius assertion proves the geometry
side of the WCAG 1.4.11 contract; the fill-token assertion proves the
colour side. Together they catch an accidental "neutralise the dot"
diff (e.g. swap to var(--c-ink-3) or a literal light token) before the
permanent axe-core gate ships in #692.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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

@@ -342,6 +342,13 @@ describe('StammbaumTree viewBox', () => {
 		const dot = document.querySelector('svg circle');
 		expect(dot).not.toBeNull();
 		expect(dot!.getAttribute('r')).toBe('6');
+		// Cycle-2 follow-up from Sara: codify the colour-token side of the
+		// WCAG 1.4.11 contrast contract at the unit level. The permanent axe-
+		// core gate lives in #692; this assertion prevents an accidental
+		// "neutralise the dot" diff (e.g. swap to var(--c-ink-3) or a literal
+		// light token) from stripping the 3:1 contrast guarantee before #692
+		// ships.
+		expect(dot!.getAttribute('fill')).toBe('var(--c-primary)');
 	});
 
 	it('centers two spouse nodes within the minimum viewBox', async () => {