Purchase order approval thresholds

All POs over $5,000 require accounting_manager approval before sending to the vendor.

Thresholds:

• Under $1,000: anyone with purchase_order:write
• $1,000–$5,000: operations_manager or above
• Over $5,000: accounting_manager required
• Over $25,000: admin required AND a written quote attached

These thresholds are enforced as Business Rules; see /business-rules.