[chore/frontend] use localized time string in status & poll info page

[cdn0x12]

Description

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This PR makes a workaround to display timestamps in the user's local timezone:

Precise timestamps (containing hours and minutes) now converted to user's local time using browser's toLocaleString(), while vague timestamps (e.g. "Dec, 2024") are unchanged

Currently, the timestampPrecise in the Template has been removed because there's no need to return the server's local time right now. However, the corresponding field in template.go is still retained because I'm not sure if we might need it elsewhere.

The time format that users actually use might differ from the originally defined format. For example, it might now display as 12/31/2024, 11:11:11 PM instead of Dec 31, 2024, 23:11. It seems that some browsers convert it to a format like 2024-06-06T00:33:54.427Z, so I'm explicitly specifying it to match the timestampPrecise format.

Other parts of the settings panel already use toLocalString, so I didn't make any changes there.

closes #3819

Checklist

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