The quick-add sheet no longer closes on every save: a new 'Save & add
another' action saves the seed, clears the form (keeping the chosen lot
type), refocuses the name field and shows an 'N added' running count, so
a whole shelf can be entered without reopening the sheet each time.
Plain Save still closes it. Adds a dedicated label field with its own
controller, submitAndAddAnother() on the cubit, and cubit + widget tests.
