## Problem
The Codex TUI session picker displays session Created and Updated timestamps in UTC, even when the operating system is configured for China Standard Time (UTC+8 / Asia/Shanghai).
For users in UTC+8, the displayed times are eight hours behind local time and can be confusing when reviewing recent sessions.
## Requested feature
Add a persistent timezone setting for Codex session timestamps. For example:
```toml
timezone = “Asia/Shanghai”
```
The exact configuration shape can be chosen by the maintainers. The setting should apply to the session picker and other Codex surfaces that display timestamps.
## Expected behavior
- Accept IANA timezones such as Asia/Shanghai.
- Keep UTC as the default for backward compatibility, or provide an explicit local-time option.
- Validate invalid timezone values with a clear configuration error.
- Document the setting and its default.
- Add tests covering UTC and UTC+8 display.
## Environment
- OS timezone: Asia/Shanghai (UTC+8)
- Interface: Codex TUI session picker
- Affected fields: Created and Updated
This is a usability issue for users working outside UTC and would also benefit users in other time zones.