Delete a finished Job and erase its data

Erases a terminal job’s input snapshot and result bytes now and keeps a minimal durable tombstone for usage, audit and idempotency. After it, GET answers 404 JOB_NOT_FOUND and a request reusing the job’s Idempotency-Key answers 410 JOB_DELETED; the key stays claimed until its retention ends. A queued or running job answers 409 JOB_IN_PROGRESS: cancel it and wait first. Usage already recorded for the job is unchanged. Idempotent: a repeat answers 204. Requires the scope of the job’s operation.