test(frontend): update mock data for displayName and nullable firstName

Add displayName and personType to all Person mock objects in
component and page tests. Update assertions from reversed
"lastName, firstName" format to forward-order displayName.

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

frontend/src/routes/persons/page.svelte.spec.ts

@@ -11,6 +11,7 @@ const makePerson = (overrides = {}) => ({
 	id: '1',
 	firstName: 'Max',
 	lastName: 'Mustermann',
+	displayName: 'Max Mustermann',
 	documentCount: 0,
 	...overrides
 });