BLU Studio · upload endpoint

POST /upload
  Headers:
    Authorization: Bearer <dealership-token>
  Multipart form fields:
    stockNumber   string  (5-9 alphanumeric, ≥3 digits, uppercased)
    phase         string  (pre | pro)
    photos        File    (repeat for each photo, max 15 pre / 36 pro)

Upload protocol:
  1. PRUNE existing STOCK_*.jpg files on DriveHQ for the stock #
  2. STAGE every new photo as STOCK_NN.jpg.tmp via WebDAV PUT
  3. COMMIT by MOVEing each .tmp to its final .jpg name

vAuto polls DriveHQ via SFTP on its normal cadence (~15–60 min).