Date group title in web timeline confuses time zones

[C-Otto]

The bug

See #12650 (comment) and #12650 (comment)

The date shown for the group may be "today" or "yesterday". This is determined based on the comparison of "now" and the asset's date, truncated to midnight (start of the day). During this, the asset date's local time is used (which is UTC from a technical point of view), whereas the browser time (now) might include time zone offset information. As a result of this, an asset created today, having the "localDateTime" of today, might be shown as "yesterday" or "tomorrow".

web/src/lib/utils/timeline-util.ts:98

Version of Immich Server

v1.125.2

Platform with the issue

• Server
• Web
• Mobile

Reproduction steps

• modify asset time to today's date, 00:00:00 in time zone Pacific/Honolulu
• set server's time zone to Pacific/Honolulu (TZ in .env)
• set browser system's time zone to Pacific/Honolulu timedatectl set-timezone Pacific/Honolulu
• set local time to 13:59:00 date -s "2025-xx-yy 13:59:00"
• see image show as "today"
• wait until time is 14:00 (which is midnight UTC)
• see image show as "yesterday"