Record a vendor check

Record a hand-written vendor check (no OCR). With billId the check allocates through postBillPayment; without a bill it posts DR expense / CR bank through postCheckPayment. Both paths create a payment row (type made, method check) and exactly one vendor_check with status recorded. newVendorName creates a supplier contact inline, but a normalized-key match against existing vendors returns 409 duplicate_vendor with the matches for an explicit choice instead of auto-creating a duplicate. Requires the manage:payments role and an idempotency-key header.