fix: use UTC-aware timestamps in mqtt_uploader.py

[LaurisGale]

mqtt_uploader.py uses datetime.now().isoformat() in three places, which produces naive local-time timestamps with no timezone indicator (e.g. 2026-06-04T23:46:42.123456). On any Home Assistant host running in a non-UTC timezone, these timestamps are offset from UTC but carry no suffix to indicate that — so receiving brokers have no way to interpret them correctly.

This causes the following error on MeshCore-compatible brokers (e.g. CoreScope / LetsMesh(?) ):

Naive observer clock — timing is being clamped
This observer is emitting zone-less local-time timestamps and its clock is
currently Xh ahead of UTC. Per-packet rxTime for this observer is being
collapsed to ingest time, which muddies propagation-delay analytics.

Note: logbook.py is unaffected — it already correctly uses dt_util.utcnow().

Fix

Import timezone from the standard library and pass it to all three datetime.now() calls in mqtt_uploader.py:

# Before
from datetime import datetime
...
datetime.now().isoformat()   # lines 822, 1019, 1148

# After
from datetime import datetime, timezone
...
datetime.now(timezone.utc).isoformat()   # lines 822, 1019, 1148

This produces offset-aware ISO 8601 timestamps (e.g. 2026-06-05T17:46:42.123456+00:00) that brokers can unambiguously interpret as UTC.

Files changed

• custom_components/meshcore/mqtt_uploader.py — 4 lines (1 import, 3 call sites)

Testing

Reproduced on a Home Assistant host in Europe/Vilnius (UTC+3). After this fix, broker clamp events stop and the error banner clears within 24 hours.