Support BYHOUR in automation RRULE schedules

Summary

Please allow Codex automation schedules to accept BYHOUR in RRULE definitions.

Motivation

Automation scheduling currently supports recurring schedules, but RRULEs that include BYHOUR appear to be rejected. This makes it harder to express common schedules directly, especially when users want a recurring task at a specific hour without relying on a more limited schedule shape.

Example

A schedule like this should be accepted:

FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR;BYHOUR=9;BYMINUTE=0

Expected behavior

Codex automations should parse and accept valid RRULE schedules that include BYHOUR, and run the automation at the specified hour according to the user's configured timezone.

Actual behavior

Schedules containing BYHOUR are currently not accepted.

Use case

This would make automation scheduling more expressive and closer to standard RRULE semantics, allowing users to define precise hourly constraints for weekly or daily recurring automations.