Delete Portfolio Asset

Deletes the R2 object and its metadata row. `data` is `null` on success. Session-authenticated only. This does not rewrite any portfolio that still references the asset — remove the reference and save the draft first, or publishing will fail with `400`.

curl -X DELETE "https://example.com/api/v1/portfolio-assets/string"

{  "success": true,  "message": "Success",  "data": null}