Manual timezone is the single source of local-time truth (task 7e173881) (#285)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

tests/test_api_admin_snapshot.py

@@ -37,7 +37,7 @@ from zoneinfo import ZoneInfo
 
 import pytest
 
-from api import routes_admin, routes_panel
+from api import host_zone, routes_admin, routes_panel
 from api.nestquest_core import core_snapshot
 from tests.admin_jwt_harness import (
     ADMIN_KEY,
@@ -101,6 +101,8 @@ async def snapshot_household(
 
     monkeypatch.setattr(routes_admin, "_local_now", _admin_now)
     monkeypatch.setattr(routes_panel, "_local_now", lambda: pinned_now)
+    # The API host runs UTC, the zone of the pinned clock.
+    monkeypatch.setattr(host_zone, "host_timezone", lambda: "UTC")
     runner = AdminRunner(temp_db_path, jwks_for(ADMIN_KEY, KID))
     async with runner as client:
         yield SimpleNamespace(
@@ -165,7 +167,10 @@ async def test_admin_jwt_returns_documented_snapshot(
 
     Every field is asserted as an explicit literal, with ONE clock
     read for the request.  With no missed view in the real snapshot,
-    the admin body equals the panel body for the same household.
+    the admin body equals the panel body for the same household — the
+    panel body additionally carries the effective ``timezone`` its cards
+    format the visible date and clock in (none stored here: the UTC
+    host's own zone).
     """
     client = snapshot_household.client
     seed = snapshot_household.seed
@@ -241,7 +246,7 @@ async def test_admin_jwt_returns_documented_snapshot(
         "/api/v1/panel/snapshot", headers=_panel_headers()
     )
     assert panel.status_code == 200
-    assert panel.json() == body
+    assert panel.json() == {**body, "timezone": "UTC"}
 
 
 async def test_admin_keeps_missed_instance_panel_omits_it(