## Why

When Outlook Classic detects the current Teams appointment at transcription start, Meeting Assistant already copies title, attendees, and agenda into meeting artifacts. The assistant context should also record the appointment's scheduled end time so later agent steps can understand meeting timing without querying Outlook again.

## What Changes

- Add `scheduled_end` frontmatter to assistant context notes when a Teams appointment is detected at recording start.
- Preserve `scheduled_end` when assistant context state changes.
- Keep the field absent when no Teams appointment is detected.

## Impact

- Affected specs: meeting-summary, meeting-session
- Affected code: Outlook meeting metadata, recording coordinator, assistant context artifact store