feat: add What's new feature

Dashboard dialog shows unseen news entries. Users mark them seen with "Got it"
or revisit via the /whats-new page. Admins publish, edit, and delete entries
on /admin/news. Full i18n support and test coverage included.

src/components/AppHeader.test.jsx

@@ -54,6 +54,7 @@ describe('AppHeader', () => {
         openMenu();
 
         expect(await screen.findByText('NAV.ADMIN')).toBeTruthy();
+        expect(screen.getByText('NAV.ADMIN_NEWS')).toBeTruthy();
         expect(screen.getByText('NAV.VIEW_AS.MENU')).toBeTruthy();
         expect(screen.queryByText('NAV.VIEW_AS.BADGE')).toBeNull();
         expect(screen.queryByLabelText('NAV.PENDING_REQUESTS:0')).toBeNull();
@@ -92,7 +93,9 @@ describe('AppHeader', () => {
         openMenu();
 
         expect(await screen.findByText('NAV.SETTINGS')).toBeTruthy();
+        expect(screen.getByText('NAV.WHATS_NEW')).toBeTruthy();
         expect(screen.queryByText('NAV.ADMIN')).toBeNull();
+        expect(screen.queryByText('NAV.ADMIN_NEWS')).toBeNull();
         expect(screen.queryByText('NAV.VIEW_AS.MENU')).toBeNull();
     });
 });