In-app announcements for new features

Right now, announcements about new features only live on the community site, so users that don't check it regularly discover changes by running into them.

Request: surface new feature announcements inside Hudu itself.

• A noticeable in-app indicator (toolbar icon or dashboard tile) when there are unread announcements. Subtle animation is what catches the eye. Clicking opens a list of recent changes.

• An optional guided tour launched from that indicator, with dismiss and "remind me later" options so it doesn't interrupt work.