The core user-generated content. - [ ] `upsertReview(albumId, rating, text, userId, displayName)` - max one per user per album - [ ] `deleteReview` - [ ] star rating as a **radio group** so it is keyboard- and screen-reader-operable - [ ] inline error if saving fails; `role="alert"` **Acceptance:** a saved review survives a reload and appears attributed to the right display name.