agent_ui: Fix thread history item showing GMT time instead of local time on Windows (#42198)

Closes #42178
Now it's consistent with the DateAndTime path which already does
timezone conversion.

- **Future Work**
Happy to tackle the TODO in `time_format.rs` about implementing native
Windows APIs for proper localized formatting (similar to macOS's
`CFDateFormatter`) as a follow-up.

Release Notes:

- agent: Fixed the thread history item timestamp, which was being shown
in GMT instead of in the user's local timezone on Windows.
a3f04e8b36Abul Hossain Khan committed on 11/10/2025, 4:34:59 PM· committed by GitHubparent3c81ee6
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