Start subscriptions TSV export (async)

Queue a background job that exports the entire filtered subscription set as a TSV file (UTF-8 BOM, tab-delimited, Excel-friendly). Useful when the dataset is too large to page through /subscriptions/list.

The endpoint returns immediately with status: "pending" and an id. Poll GET /exports/{id} until status == "completed", then fetch download_url (signed, expires in 1 hour).

Accepts the same filters as /subscriptions/list. All filters are optional — omit them to export everything in the project.

{
  "from": "2026-01-01",
  "to": "2026-05-20"
}

{
  "success": 1,
  "export": {
    "type": "subscriptions",
    "file_name": "subscriptions_export_2026-05-20_18-30-00.tsv",
    "file_size_human": "12.4 MB",
    "mime_type": "text/tab-separated-values"
  }
}