Mirrors the existing /api/purchase-orders/upload pattern onto the
delivery-note path so byte-identical re-uploads short-circuit with
`200 + { duplicate: true, existing_dn_id, ... }` instead of
creating a second delivery_notes row.
Concretely:
- Hash the bytes with SHA-256 before any PB round-trip.
- Query `data_import_batches` for any processed batch with the same
hash inside a 30-day window (the same window the PO route uses; the
underlying `idx_batches_file_hash` index already covers it).
- On hit, return the existing DN + batch ids and skip creation. The
n8n OCR pipeline is never invoked for a duplicate slip, so a
double-clicking operator costs us nothing.
- On miss, stamp `file_hash` on the new batch row so subsequent
re-uploads can dedup against it.
- Wire the response through `UploadDeliveryNoteButton` as a new
'duplicate' panel showing the existing DN id plus a quick link to
/dashboard/purchasing where the awaiting-PO inbox lives.
pb-types: adds file_hash?: string to DataImportBatchRecord so the
column the PB schema already has is reflected in the TS shape.
78fa8da05c