Assign a program from the client list

The "Assign program" item in each client's row menu used to be greyed out. Now it opens a small dialog: pick one of your programs, choose a start date (today by default), and the client is on it. If they were already on a different program, that one rolls over to completed automatically — one active program per client at a time.

Works the same on mobile (long-press a client card) and desktop (the row's three-dot menu).