fix(stammbaum): keep dimmed nodes opaque so connectors do not bleed through (#703)

Group opacity on the node <g> made the whole node translucent — including
its card fill — so the connector lines drawn beneath a dimmed node showed
through it. Render the card fill at full strength outside the dim group and
move the lineage focus+dim onto an inner content group (outline + labels)
only. The focus ring also leaves the dim group, so a dimmed-but-focused
node keeps a full-strength ring.

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

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

@@ -940,10 +940,27 @@ describe('StammbaumTree lineage highlight (#703)', () => {
 		edge('mutter', 'kind', 'PARENT_OF')
 	];
 
+	// The lineage dim lives on the inner content group (outline + labels); the
+	// card fill renders outside it at full strength so connectors beneath never
+	// bleed through a dimmed node.
 	function nodeOpacity(displayName: string): string | null {
+		const content = nodeContentGroup(displayName);
+		return content.getAttribute('opacity');
+	}
+	function nodeContentGroup(displayName: string): Element {
 		const g = document.querySelector(`g[role="button"][aria-label="${displayName}"]`);
 		if (!g) throw new Error(`No node group rendered for ${displayName}`);
-		return g.getAttribute('opacity');
+		const content = g.querySelector('g.lineage-fade');
+		if (!content) throw new Error(`No content group rendered for ${displayName}`);
+		return content;
+	}
+	/** The opaque card fill is a direct-child rect of the node, outside the dim group. */
+	function cardFillIsOpaque(displayName: string): boolean {
+		const g = document.querySelector(`g[role="button"][aria-label="${displayName}"]`);
+		if (!g) throw new Error(`No node group rendered for ${displayName}`);
+		const fill = g.querySelector(':scope > rect');
+		if (!fill) throw new Error(`No card-fill rect rendered for ${displayName}`);
+		return fill.getAttribute('opacity') === null && fill.getAttribute('fill-opacity') === null;
 	}
 	const DIM = '0.4';
 
@@ -974,8 +991,11 @@ describe('StammbaumTree lineage highlight (#703)', () => {
 		for (const name of ['Vater', 'Grossvater', 'Grossmutter', 'Kind', 'Mutter']) {
 			expect(nodeOpacity(name)).toBeNull();
 		}
-		// The collateral sibling dims.
+		// The collateral sibling dims — but its card fill stays opaque so the
+		// connectors drawn beneath it do not show through (the dim is on the
+		// outline + labels only).
 		expect(nodeOpacity('Tante')).toBe(DIM);
+		expect(cardFillIsOpaque('Tante')).toBe(true);
 	});
 
 	it('recomputes the highlight for a newly selected person and clears the previous one (AC6)', async () => {