feat(procurement): canonical consolidation for suppliers, PO lifecycle, and GRN

[rmak78]

Summary

This PR creates a single canonical procurement implementation that supersedes overlapping work in #13 and #17.

Included

• Supplier + PO + GRN baseline from the procurement track
• Supplier payment terms extension (payment_terms_note)
• PO lifecycle transition endpoint: POST /v1/purchase-orders/transition
• PO status summary endpoint: GET /v1/purchase-orders/summary
• PO status event logging table: purchase_order_status_events
• Clean migration numbering by adding 0008_procurement_po_lifecycle.sql on top of 0007

Supersedes

• feat(procurement): PR #12 Track A suppliers + PO + GRN baseline #13
• feat(procurement): PO lifecycle transitions, supplier terms, and summary endpoint #17

Validation

• npx wrangler deploy --dry-run ✅

Notes

• No duplicate procurement tables or duplicate procurement endpoints were introduced in this branch.