Add an accessible form where users can report a sighting. Depends on: Add a createSighting mutation, Add Apollo Client to the frontend ## Tasks - [ ] Form with labels, keyboard support and visible focus - [ ] Client-side validation with clear error messages - [ ] Success and error feedback after submitting - [ ] New sightings show up in search and on the detail page ## Done when A user can submit a sighting using only the keyboard and then find it in the list.