Update wire protocol to version 6 and enhance timetable functionality

- Bumped the wire protocol version to 6, reflecting changes in the communication structure.
- Expanded the timetable API with new endpoints for fetching and managing lesson schedules, including `GET /api/schools/{id}/timetable` and `POST /api/schools/{id}/timetable/pin`.
- Updated the protocol documentation to include detailed descriptions of the new timetable features and message structures.
- Enhanced the client-side implementation to support the new timetable functionalities, including lesson pinning and unpinning.
- Revised server-side logic to handle timetable operations and ensure proper integration with existing school management features.
- Added tests to validate the new timetable functionalities and ensure robustness in handling lesson data.

docs/phases/README.md

@@ -66,5 +66,5 @@
 | --- | --- | --- |
 | [14. Каркас дня и каникулы](14-school-calendar.md) | ✅ | Звонки, длина недели, каникулы |
 | [15. Планировщик](15-timetable-planner.md) | ✅ | Раскладка часов по слотам, четыре запрета |
-| [16. Расписание в школе](16-timetable-in-school.md) | ⬜ | Сейв, снимок, «кто где сейчас» |
+| [16. Расписание в школе](16-timetable-in-school.md) | ✅ | Сейв, снимок, «кто где сейчас» |
 | [17. Расписание на экране](17-timetable-screen.md) | ⬜ | Скобки в дереве, сетка класса, расписание учителя |