Add "Plain UTC" Option to User Time Zone Selection

[germanosin]

Issue submitter TODO list

• I've searched for an already existing issues here
• I'm running a supported version of the application which is listed here and the feature is not present there

Is your proposal related to a problem?

No response

Describe the feature you're interested in

Currently, the user time zone selector does not include a straightforward "UTC" option. To improve usability and support users who prefer a standardized, non-localized time reference, we should add a "Plain UTC" (Coordinated Universal Time) entry to the list of selectable time zones.

Acceptance Criteria:

• A "UTC" or "Plain UTC" option appears in the time zone dropdown.
• The option should be clearly labeled and easy to find.
• Selecting this option sets the user's time zone to Coordinated Universal Time (UTC+00:00).

Describe alternatives you've considered

No response

Version you're running

1.3.0

Additional context

No response