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.