Restore Campaign Drafts

Bring removed drafts back.

Not reachable from the UI. Any content writer on the profile may call it (the same gate as removal: it undoes a soft delete in their own workspace), which is how an operator brings a removal back. A user_requested tombstone is restorable for as long as it exists.

Like the bulk delete, each target commits on its own and reports its own outcome: one that fails unexpectedly is logged and answered error while the rest are still tried, so an earlier restore is never hidden behind a 500.