fix(periodic-report): accept UTC without tzdata

[Duang777]

Summary

• treat canonical UTC as valid without requiring an external IANA timezone database
• preserve strict ZoneInfo validation for every other timezone
• cover Windows-style missing-tzdata behavior with a regression test

Root cause

The Windows packaged install has no external tzdata package. Validating the built-in UTC periodic-report default through ZoneInfo raised ZoneInfoNotFoundError, so quota should-run failed closed. This is the shared baseline failure currently visible on #4204 and #4133.

Validation

• 45 focused periodic-report/configuration tests passed
• scoped Ruff passed
• full mypy passed
• git diff --check passed
• the same fix previously passed the Windows PowerShell job on build: bound retained chat assets #4233 exact head 06699be

[Duang777]

@huangruiteng This is the isolated fix for the Windows failure currently present on main@787e8dd83 and inherited by PR #4233. The critical windows-powershell check passes on exact head 3a718ae517c1c425fe88f709b53d914e3607816b; remaining checks are still running. Please review when complete.

[Duang777]

@huangruiteng Exact head 3a718ae is now fully green: 23 checks passed and 4 expected skips, including Windows PowerShell, four pytest shards, Stage2C, compatibility, dashboard, DCO, and merge-gate. This 3-file baseline fix unblocks #4233, #4204, and #4133, whose current only substantive CI failure is the same missing-tzdata UTC path. Please prioritize independent review/merge of #4281; after it lands I will resync those three PRs to main and rerun their CI.

[Duang777]

@huangruiteng Main advanced to 6ef6838, so #4281 is now synchronized at exact head 89a50b8. The merge was clean; the 3-file diff is unchanged. Revalidation: 45 focused tests, scoped Ruff, full mypy, and git diff --check all passed. Fresh exact-head CI is running.

[Duang777]

@huangruiteng Exact head 89a50b8 is now fully green on main 6ef6838: 23 checks passed and 4 expected skips, including Windows PowerShell and required merge-gate. This is the minimal shared baseline fix needed before #4233, #4204, and #4133 can be resynced without scope drift.

[Duang777]

Closing as superseded by #4263, which is now on main and includes the same canonical UTC-without-tzdata behavior plus a Windows regression test. The current main code already skips external ZoneInfo lookup for UTC, so merging #4281 would duplicate the fix and regress newer periodic-report schedule work.