Clear the shop's do-not-contact list

Remove every creator from this shop's blacklist in one call, making all of them eligible for outreach again.

There is no undo — the rows are deleted, not archived, so read the list with GET /shops/blacklist first if you may need to restore it. Clearing an already-empty list is a no-op that returns removed_count: 0. Requires a key with read_write scope and a single shop.