Improve timestamp handling and event navigation

server/monlet_server/api/checks.py

@@ -6,6 +6,7 @@ from ..cursors import decode, encode
 from ..db import get_session
 from ..models import Check
 from ..schemas import ID_PATTERN, ChecksPage, CheckState
+from ..timeutil import to_utc
 
 router = APIRouter()
 
@@ -38,7 +39,7 @@ async def list_checks(
             agent_id=r.agent_id,
             check_id=r.check_id,
             status=r.status,
-            last_observed_at=r.last_observed_at,
+            last_observed_at=to_utc(r.last_observed_at),
             exit_code=r.exit_code,
             incident_key=r.incident_key,
         )