fix(opencode): respect system locale for time formatting

[jeaEmri]

Issue for this PR

Closes #28804

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Bun ignores LC_TIME/LANG env vars when undefined is passed to toLocaleTimeString(), defaulting to en-US (12h AM/PM) regardless of system locale. This is a known Bun bug (oven-sh/bun#7386, open since Dec 2023).

The fix adds a small helper that reads POSIX locale env vars (LC_ALL > LC_TIME > LANG), converts the value to BCP-47 format (e.g. da_DK.UTF-8 -> da-DK), and passes it explicitly to toLocaleTimeString() and toLocaleDateString(). Falls back to undefined (current behavior) when no env vars are set.

How did you verify your code works?

• bun test test/util/locale.test.ts -- 3 tests pass (24h locale, 12h locale, no-env fallback)
• Manual verification: LC_TIME=da_DK.UTF-8 bun -e "..." confirms 08.xx output vs 8:xx AM without the fix

Screenshots / recordings

Not a UI change -- only affects time string formatting logic.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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