Upload bytes to the relay so they can be pushed to a machine

PRO ONLY: Free and anonymous callers cannot upload. Stores the raw FILE body (--data-binary @localfile, not JSON) as a temporary blob for /api/v1/push. Limit 100 MiB; access ends 24 hours after upload even after downgrade, followed by retrying cleanup. Content-Length is mandatory: missing returns 411 before reading, a declared length over the cap returns 413, and a body whose actual length differs returns 400 with nothing stored. Allowed uploads are limited to 60/hour/account, 5000/hour relay-wide, and share a 5 GiB/account/rolling-day storage budget with pulls. Over quota returns 429 rate_limited.