We should store timestamps internally as UTC

[u10313335]

Describe the bug

We don't store the zone information in the log. So if we store a localized time, it will be displayed incorrectly.

To Reproduce

Any timestamps in the log.

Expected behavior

We should show the time correctly.

Additional context

A similar issue and fix in the ckanext-xloader: ckan/ckanext-xloader@67c871d

[jqnatividad]

Status check against current main (59e08d7): partially addressed, two sites still drift.

Already UTC:

• utils.py:34 — uses datetime.datetime.now(datetime.timezone.utc).replace(tzinfo=None) (correct UTC; tzinfo strip is only because the column type is TIMESTAMP WITHOUT TIME ZONE).
• cli.py:452, logic/action.py:101,132,230,264 — use datetime.datetime.utcnow() (naive UTC; works but utcnow is deprecated in 3.12+).

Still on local time (the original bug from this issue):

• helpers.py:345 — "finished_timestamp": datetime.datetime.now()
• helpers.py:364 — "finished_timestamp": datetime.datetime.now()

These two are the user-visible timestamps in the job-status UI panel and will silently report local-tz on whatever host the worker runs on, not UTC. A focused fix would: (a) switch both to datetime.now(tz=timezone.utc).replace(tzinfo=None) for consistency with utils.py, (b) replace the utcnow() calls with the same idiom to drop the deprecation warning, (c) update the surrounding code that reads these to format them as "... UTC" for clarity in the UI.

Leaving open — it's a small focused fix anyone can pick up.