refactor(stammbaum): extract RelationshipChip and AddRelationshipForm

Split StammbaumCard from 366 to 196 lines by extracting:
- RelationshipChip.svelte — single relationship list item with optional delete
- AddRelationshipForm.svelte — self-contained add-relationship form with open/close state

Both components have browser-mode spec tests covering rendering and interaction.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/AddRelationshipForm.svelte.spec.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect, afterEach, vi } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import AddRelationshipForm from './AddRelationshipForm.svelte';
+
+vi.mock('$app/forms', () => ({ enhance: () => () => {} }));
+vi.mock('$lib/components/PersonTypeahead.svelte', () => ({ default: () => null }));
+
+afterEach(cleanup);
+
+describe('AddRelationshipForm', () => {
+	it('shows add-relationship button initially and no form', async () => {
+		render(AddRelationshipForm, { personId: 'person-1' });
+		await expect.element(page.getByRole('button')).toBeInTheDocument();
+		await expect.element(page.getByRole('combobox')).not.toBeInTheDocument();
+	});
+
+	it('shows relationType select when add button is clicked', async () => {
+		render(AddRelationshipForm, { personId: 'person-1' });
+		document.querySelector<HTMLButtonElement>('button')!.click();
+		await expect.element(page.getByRole('combobox')).toBeInTheDocument();
+	});
+
+	it('hides form and shows button when cancel is clicked', async () => {
+		render(AddRelationshipForm, { personId: 'person-1' });
+		document.querySelector<HTMLButtonElement>('button')!.click();
+		await expect.element(page.getByRole('combobox')).toBeInTheDocument();
+		const cancelBtn = [...document.querySelectorAll<HTMLButtonElement>('button')].find(
+			(b) => b.type === 'button' && /abbrechen/i.test(b.textContent ?? '')
+		);
+		cancelBtn!.click();
+		await expect.element(page.getByRole('combobox')).not.toBeInTheDocument();
+	});
+
+	it('submit is disabled when no person is selected', async () => {
+		render(AddRelationshipForm, { personId: 'person-1' });
+		document.querySelector<HTMLButtonElement>('button')!.click();
+		await expect.element(page.getByRole('button', { name: /^Hinzufügen$/i })).toBeDisabled();
+	});
+});