Register a file in a space and get a presigned upload URL

Reserves a file metadata record in the space and returns { id, uploadUrl, uploadExpiresAt, file }. `uploadUrl` is a secure PUT URL valid for 15 minutes (see `uploadExpiresAt`, ISO 8601). Two-step upload: PUT the raw file bytes to `uploadUrl` with a `Content-Type` request header EXACTLY equal to the `mimeType` you sent at create (a mismatch rejects the PUT), then poll `getFile` until `status` reaches a terminal value — `stored` (uploaded, no processing requested), `processed` (processing succeeded), or `failed` (see `processingError`); `waiting`/`processing` mean keep polling. Request body: `fileName` (required), `mimeType` (required, drives both the record and the required PUT Content-Type), `size` (bytes, optional), optional `processingKind` — one of doc-simple | doc-ocr | doc-auto | audio-transcribe | audio-transcribe-and-diarize — selecting how the stored file is post-processed; `indexVectors` and `indexOntology` (both default true) are opt-out booleans for semantic and ontology indexing. `parentType`/`parentId` in the body are ignored: the API forces the parent to this :spaceId. Authorization: requires `space:contribute` on :spaceId (missing permission → 403; org admins bypass). An invalid body returns 422.