Procurement: create multiple orders at once (one per distributor)

What: When selected pending items span multiple distributors, allow creating all purchase orders in one action — one PO per distributor — instead of greying out the button.

Current behavior: Selecting items from more than one distributor greys out "Add to Order", forcing the user to select and submit per distributor, one at a time.

Desired behavior: With a mixed-distributor selection, "Add to Order" stays enabled and splits the selection automatically into one order per distributor (with a confirmation of the split before submitting).

Note: recreated after accidental deletion — originally filed 2026-07-08.