fix(campaign): roll back rejected immediate queues

src/govoplan_campaign/backend/router.py

@@ -3608,6 +3608,10 @@ def send_campaign_now_endpoint(
         )
         return SendCampaignNowResponse(result=response_result)
     except SynchronousSendRejected as exc:
+        # A synchronous request stages queue state before the all-message
+        # preflight can run. Rejecting that preflight must not leave work
+        # eligible for a background worker when no provider effect occurred.
+        session.rollback()
         audit_from_principal(
             session,
             principal,