v1.9.0

v1.9.0 — Multi-source shipment fan-out + line-item association (#6)

Fans tracking-number adds on fulfillment orders out to every source order in _fishotel_fulfillment_sources so customer emails actually reach the buyer, adds a line_item_ids column (DB 1.2.0) so partial fulfillments only list/transition/auto-complete the items in that box, allows duplicate tracking numbers across different source orders, and ships kill switches (FST_FULFILLMENT_FANOUT_OFF constant or fst_fulfillment_fanout_enabled=0) to restore pre-1.9 behavior.