test(persons): convert .not.toThrow self-skip test into Self-letter rendering assertion

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

frontend/src/routes/persons/[id]/page.svelte.test.ts

@@ -135,8 +135,9 @@ describe('persons/[id] page', () => {
 				}
 			]
 		});
-		// Just verify the page renders without error — the self-skip branch is exercised
-		expect(() => render(PersonDetailPage, { props: { data } })).not.toThrow();
+		// Self-skip branch: the self-letter is rendered without re-rendering the sender chip.
+		render(PersonDetailPage, { props: { data } });
+		expect(document.body.textContent).toContain('Self-letter');
 	});
 
 	it('renders the GeschichtenCard when geschichten array has items', async () => {