Maintenance windows could disappear seconds after creation when the API received
a payload with end dates already in the past. The repository auto-set
expiry = end for one-time windows (repeat = 0), and Mongo's TTL index on the
expiry field then deleted the row on its next sweep. This was particularly
visible with automation tools sending payloads in non-UTC timezones.
## Changes
### Validator hardening
- Add .strict() to create + edit body schemas so unknown keys return 400
instead of being silently dropped.
- Refine end > start on create.
- Refine end > now for one-time create payloads (repeat = 0).
- Refine end > start on edit when both are provided.
- Remove the accepted expiry field from both schemas.
### Stop the auto-delete behaviour
- Repository.create no longer copies end into expiry.
- Schema's expiry field + TTL index removed.
- Migration 0007 drops the live TTL index and unsets stale expiry values on
existing rows so legacy data is no longer at risk.
### Client
- Form submission no longer includes expiry.
gorkem-bwl
Alex Holliday