chore(backend): move import json to module top in store.py

backend/src/cyclone/store.py

@@ -28,6 +28,7 @@ Backward-compat shims for tests that relied on the in-memory internals:
 
 from __future__ import annotations
 
+import json
 import threading
 from datetime import datetime, timezone
 from decimal import Decimal
@@ -193,13 +194,6 @@ def _remittance_835_row(cp: ClaimPayment, batch_id: str) -> Remittance:
     )
 
 
-# ``json`` is imported lazily inside the helpers above so we don't pull
-# the stdlib ``json`` into module-level imports at the very top — keeps
-# the dependency surface easy to audit. The ``import json`` line below
-# is the actual import used by the helpers above.
-import json  # noqa: E402
-
-
 # ---------------------------------------------------------------------------
 # UI mappers: ORM rows → simpler UI types.
 # ---------------------------------------------------------------------------