Upload a file for workflow inputs

Use file upload when your images, videos, audio, or subtitle files are not already hosted at public HTTPS URLs. The returned HTTPS URL can be used directly in `images`, `reference_videos`, `audio_url`, or `srt_url`. Limits: - Images, audio, and subtitles: maximum 50 MB. - Motion videos: maximum 100 MB. - Images: `png`, `jpg`, `jpeg`, `webp` (`image/png`, `image/jpeg`, `image/webp`). - Audio: `mp3`, `wav`, `aac`, `m4a` (`audio/mpeg`, `audio/wav`, `audio/aac`, `audio/mp4`). - Audio uploads must be 10-300 seconds. The selected Music Video tier applies its own task limit: Standard 10-180 seconds; Premium 10-300 seconds. - Motion videos: `mp4`, `mov` (`video/mp4`, `video/quicktime`), 3-30 seconds. Duration and dimensions are detected during upload. - Subtitles: `srt` (`application/x-subrip`; multipart uploads may use `text/plain` only when the filename ends in `.srt`). - PDF, generic text files, octet-stream uploads, Matroska videos, and zip files are not supported for launch. - Send either multipart form-data with a `file` field, or send the raw file body with the asset `Content-Type`. - `Content-Length` is required and is validated before BeatAPI buffers the request body; chunked uploads without a declared length are rejected. - Returned URLs are HTTPS and long-lived for launch. - Uploaded audio files are duration-checked during upload. The response includes `audio_duration_seconds` when the uploaded asset is audio. - Uploaded videos are signature-, duration-, and dimension-checked. The response includes `video_duration_seconds`, `width`, and `height`. - Workflow task inputs still require public HTTPS URLs. Localhost, private network URLs, and data URLs are not accepted.