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/utils/limits.js

@@ -30,3 +30,6 @@ export const MAX_CORRECTION_GENRES = 10;
 export const MAX_DISPLAY_NAME_LENGTH = 24;
 // Auth CreateHintRequest @Size(max = 500)
 export const MAX_HINT_LENGTH = 500;
+// Auth NewsRequest @Size(max = 100) and @Size(max = 2000)
+export const MAX_NEWS_TITLE_LENGTH = 100;
+export const MAX_NEWS_TEXT_LENGTH = 2000;