Add an Edit form bound to the tickets list

Bramblewood's app reads tickets but can't yet edit them. A full help-desk app often uses three screens (Browse, Detail, Edit); here we keep the form on DetailScreen for simplicity. A separate Edit screen is optional polish you can add later.

Add an Edit form to the Detail screen, point its DataSource at the Tickets list, and bind it to the selectedTicket row the user arrived with. By the end, every field shows in the form ready to edit, though we don't submit until the next exercise.