Platform Storage Move To Kind

Reparent an existing storage_files row into a different Apps/<App Title>[/<new_kind>]/ folder, WITHOUT moving the S3 object.

Used by per-app backends that want to reorganize files after upload — e.g. nail-art's /submit route moves user-uploaded hand / nail_set files into a job-{id}/inputs/ folder once a job_id is known.

The S3 key stays put (so presigned URLs already minted against it keep working through the move); only storage_files.folder_id + storage_files.metadata_.kind change. new_kind may contain / so apps can move into a nested per-job tree in one call.

Idempotent — if the file is already in the target folder, returns moved=false. Otherwise creates the destination folder chain (if needed) and updates the row in one transaction.

Internal-key auth. Caller supplies app_slug + installation_id so we can scope-check ownership (file must belong to the install's user / team).