Feature: Scheduled actions

I don't think we need this for MVP, but many workflows will need something like this for practical use.
- When an indebtedness check is awaiting the submitter to "resubmit" info for more than 30 days, mark it "cancelled."
- When a FOIA request hasn't been fulfilled in 5 _business_ days, send an email requesting an extension
- When a contract has been in a step for more than 2 weeks, send a reminder to the assignee

Just leaving this issue here for when it's time.

The issue names no files, tests, or entry points. Start by mapping how workflows represent waiting states and scheduled notifications, then clarify the three proposed time-based behaviors, including business-day handling and cancellation rules. Done should be defined as implemented behavior for the agreed scenarios with tests covering each timing rule.

Written by the indexing model from the issue text.