Upload bytes against a signed ticket

Authorized by the HMAC ticket in the path, not by a session or token — so an agent can hand a file to tela without the bytes passing through its context. Single use, five-minute TTL.

The ticket is minted by the MCP tool request_attachment_upload and finalized by confirm_attachment_upload; neither has a REST route, so a pure-REST client should use POST /api/pages/{id}/attachments instead.

The request body is the raw file bytes with any content type.