The other half of the market: share your marked lots as offers.
- VarietyRepository.shareableLots(): non-private lots WITH their id (stable,
updatable offer id) + the variety label. Private lots never leave the device.
- OffersCubit.publishLots(): maps each via OfferMapper and publishes, tagged
with the coarse area + signed by the derived key; counts acceptances; no-op
offline or with no area.
- Market screen: a 'share my seeds' action (online only) — publishes, then
re-discovers to show them; 'mark some seeds first' when nothing's shared.
- i18n en/es/pt.
14 tests green (repo query, cubit publish, market UI); analyzer clean for new code.
