Remove a campaign from use.

Needs the campaigns:write scope, like every campaign write.

A campaign that has run at DelivrDSP is stopped there and archived: it no longer serves or appears in the default campaign list, and its spend, budget and reporting stay readable. A campaign that never ran is deleted outright, together with its creatives. Either way, exports feeding only this campaign are paused.

Archiving an archived campaign answers 204 again, so a retry is safe. An archived campaign accepts no other write.