feat(dashboard): empty-state message for ReaderPersonChips

When the top-persons fetch returns an empty list (or fails and
degrades to []), the chip area used to render the heading and the
view-all link with nothing in between, looking like a load failure.
Adds dashboard_reader_no_persons (de/en/es) and renders it above the
chip row.

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

frontend/src/lib/shared/dashboard/ReaderPersonChips.svelte.spec.ts

@@ -78,4 +78,10 @@ describe('ReaderPersonChips', () => {
 		const chips = page.getByRole('link', { name: /Müller|Schmidt/ });
 		await expect.element(chips).not.toBeInTheDocument();
 	});
+
+	it('renders an empty-state message when persons array is empty', async () => {
+		render(ReaderPersonChips, { persons: [] });
+		const message = page.getByText(/Noch keine Personen im Archiv/i);
+		await expect.element(message).toBeInTheDocument();
+	});
 });