GeezerVison

Problem

Log Explorer and Alerts use browser-local timestamp formatting in several places instead of the timezone selected in Settings → Date & time.

Backend timestamps without an explicit timezone can also be interpreted as browser-local time instead of UTC.

Changes

• Use shared date-format preferences for log rows, expanded log headers, alert timestamps, and histogram labels.
• Apply the configured timezone to echo timeline labels and tooltips.
• Subscribe timestamp displays to preference changes, including memoized log rows.
• Interpret timezone-less backend date-time strings as UTC.
• Preserve explicit offsets and truncate sub-millisecond precision for JavaScript Date.
• Keep stored timestamps unchanged.

Validation

• All 107 frontend tests passed.
• Production build passed.
• Targeted tests also passed with TZ=America/Los_Angeles.
• Added coverage for UTC, Europe/Istanbul, America/New_York, browser-local time, date styles, and preference updates.
• Lint could not run because the repository has no ESLint configuration file.

End-to-end verification of this source change in a deployed environment is still pending.

Fixes #2897