[management] Clean up after account deletion (#7812)

Deleting an account left state behind that DeleteAccount's store
associations don't reach. The Agent Network tables outlived the account,
keeping its gateway domain claimed and its provider API keys stored. The
proxies kept serving its gateway until they next resynced. Cloud-side
state, such as managed proxy deployments, had no way to be cleaned up at
all.

Account deletion now runs registered hooks after the permission check
and before any users or data are removed. A failing hook aborts the
deletion. Agent Network registers one that tells the proxies to drop the
account's gateway mappings. The account's settings, providers, policies,
guardrails and budget rules are deleted in the account's transaction.
Consumption counters, and the access logs of deleted accounts, are left
to the background cleanup; usage records are kept.

management/server/store/sql_store_agentnetwork.go

@@ -663,6 +663,21 @@ func (s *SqlStore) IncrementAgentNetworkConsumptionBatch(
 	return nil
 }
 
+// DeleteAgentNetworkConsumptionOfDeletedAccounts deletes every consumption counter whose
+// account no longer exists and returns the number of rows deleted. Counters grow with
+// traffic, so they are swept in the background instead of in the account-deletion
+// transaction, and the sweep also catches counters a proxy writes after the deletion.
+func (s *SqlStore) DeleteAgentNetworkConsumptionOfDeletedAccounts(ctx context.Context) (int64, error) {
+	res := s.db.
+		Where("NOT EXISTS (SELECT 1 FROM accounts WHERE accounts.id = agent_network_consumption.account_id)").
+		Delete(&agentNetworkTypes.Consumption{})
+	if res.Error != nil {
+		log.WithContext(ctx).Errorf("failed to delete agent-network consumption of deleted accounts: %v", res.Error)
+		return 0, status.Errorf(status.Internal, "failed to delete agent-network consumption of deleted accounts")
+	}
+	return res.RowsAffected, nil
+}
+
 // ListAgentNetworkConsumption returns every consumption row recorded
 // for the account, ordered by window_start descending. Backs the
 // dashboard's basic counter view.