test(stammbaum): fix two CI-only browser-test failures (#692)

- page.svelte.test.ts mocked $app/navigation with only replaceState, dropping
  invalidateAll (imported by StammbaumSidePanel) → the module errored and failed
  all 7 tests in the file. Mock now exports invalidateAll + goto too.
- StammbaumTree viewBox 'offsets origin' test hard-coded a wrong unpanned-x; assert
  the robust relationship instead (viewBox centre − content centroid == pan).

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

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

@@ -54,10 +54,12 @@ describe('StammbaumTree viewBox', () => {
 		expect(w).toBe(1200);
 		expect(h).toBe(800);
 
-		// …but the origin is shifted by the pan offset.
+		// …but the viewBox centre is the content centroid shifted by the pan
-		const unpannedX = -(1200 / 2 - 160 / 2); // single 160-wide node centred
+		// offset (at pan {0,0} the centre sits on the centroid — see the test
-		expect(x).toBeCloseTo(unpannedX + 100, 6);
+		// below). This avoids hard-coding the layout's absolute coordinates.
-		expect(y).toBeCloseTo(-(800 / 2 - 56 / 2) + 40, 6);
+		const c = rectsCentroid(svg);
+		expect(x + w / 2 - c.x).toBeCloseTo(100, 6);
+		expect(y + h / 2 - c.y).toBeCloseTo(40, 6);
 	});
 
 	it('uses the minimum size and centers a single node', async () => {

frontend/src/routes/stammbaum/page.svelte.test.ts

@@ -17,7 +17,11 @@ vi.mock('$app/state', () => ({
 
 const replaceState = vi.fn();
 vi.mock('$app/navigation', () => ({
-	replaceState: (...args: unknown[]) => replaceState(...args)
+	replaceState: (...args: unknown[]) => replaceState(...args),
+	// StammbaumSidePanel (rendered transitively) imports invalidateAll/goto, so
+	// the mock must provide every export the module graph uses.
+	invalidateAll: vi.fn(),
+	goto: vi.fn()
 }));
 
 afterEach(cleanup);