## 1. Scheduled End Metadata

- [x] 1.1 Extend Teams meeting metadata with scheduled end time.
- [x] 1.2 Write `scheduled_end` to assistant context frontmatter only when Teams metadata is detected.
- [x] 1.3 Preserve `scheduled_end` across assistant context state updates.
- [x] 1.4 Add behavior tests and validate the OpenSpec change.