Add an optional PO Date field to the create and edit PO forms.
Submitters can pick any date (back-dated or forward-dated). If left
blank, the exported PO document falls back to the approved date, then
to the creation date.
Changes:
- Prisma schema: add `poDate DateTime?` to PurchaseOrder
- Migration 20260616000000_add_po_date: ALTER TABLE to add the column
- createPoSchema: add optional `poDate` string field
- new-po-form, edit-po-form: add PO Date picker in Order Information
- create/edit actions: persist poDate to DB
- edit action resubmit snapshot: track poDate changes for manager diff
- po-detail: show PO Date in Order Details; include in resubmit diff banner
- export route: use poDate ?? approvedAt ?? createdAt as the date on
the exported PDF/XLSX document
- validations.test: fix pre-existing costCentreRef→vesselId mismatch
and add poDate test cases
Fixes#4
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
25d1164d34