feat: add create person feature via web interface

- Backend: new POST /api/persons endpoint in PersonController
- Frontend: new /persons/new route with Vorname/Nachname/Alias form,
  redirects to the new person's detail page on success
- Persons list: subtle '+ Neue Person' link below the page title

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

frontend/src/routes/persons/new/+page.server.ts

@@ -0,0 +1,26 @@
+import { fail, redirect } from '@sveltejs/kit';
+import { createApiClient } from '$lib/api.server';
+
+export const actions = {
+	default: async ({ request, fetch }) => {
+		const formData = await request.formData();
+		const firstName = formData.get('firstName')?.toString().trim();
+		const lastName = formData.get('lastName')?.toString().trim();
+		const alias = formData.get('alias')?.toString().trim() || undefined;
+
+		if (!firstName || !lastName) {
+			return fail(400, { error: 'Vor- und Nachname sind Pflichtfelder.' });
+		}
+
+		const api = createApiClient(fetch);
+		const result = await api.POST('/api/persons', {
+			body: { firstName, lastName, ...(alias ? { alias } : {}) }
+		});
+
+		if (!result.response.ok) {
+			return fail(result.response.status, { error: 'Person konnte nicht gespeichert werden.' });
+		}
+
+		throw redirect(303, `/persons/${result.data!.id}`);
+	}
+};