Add notification management via two new MCP tools using the
method-dispatch pattern:
- `notification_read`: list notifications (global or repo-scoped,
with status/subject_type/since/before filters) and get single
notification thread by ID
- `notification_write`: mark single notification as read, mark all
notifications as read (global or repo-scoped)
Co-Authored-By: Claude (Opus 4.6) <noreply@anthropic.com>
