integrate: restore CostStore import dropped with #241 dual_column_view line

The #241 import resolution deleted the whole 'from cloud.cost import
CostStore, dual_column_view' line to drop the unused alias, which
also removed the CostStore import that _quota_snapshot needs; every
task creation then failed closed with 503 quota_check_unavailable
(4 EndpointChainTestCase failures in test_audit_wiring). Restored
as a plain CostStore import; dual_column_view stays available in
cloud/cost.py for #241's own tests.

cloud/server.py

@@ -63,6 +63,7 @@ from cloud.auth import ROLES as _MEMBER_ROLES
 from cloud.auth import AuthStore
 from cloud.coordinator import parse_parts as _coord_parse_parts
 from cloud.coordinator import validate_parts as _coord_validate_parts
+from cloud.cost import CostStore
 from cloud.cost import unpriced_token_cap
 from cloud.gates import merge_state_decision as _merge_state_decision
 from cloud.gates import resolve_inside as _gate_resolve_inside