Weekly purchase plan

Create a purchase order for all at risk stock

## Every Monday
1. Forecast demand for every variant through 31 Dec.
2. Flag a variant as at risk when its stock won't last its supplier's lead time plus 14 days.
3. Skip variants with an open purchase order that lands in time.
4. Size each order to cover forecast demand through 31 Dec, rounded up to the case pack.
5. Draft one purchase order per supplier.

## Approval
- Post the plan in this chat, most urgent variants first.
- Don't email a supplier until I approve.

## Flag for a second look
- Any purchase order over $20,000
- A supplier whose lead time changed since last week