The shopping_chat_autosend schedule now claims its schedule_runs period
under AutosendKey of the coming week's Monday instead of the ISO week key.
Schedule gains an optional PeriodKey hook that replaces the rule's key;
Register rejects a schedule setting both Key and PeriodKey. The fake-clock
tests assert the stored period keys.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>