Phase 3: NotificationQueue
- Add notification_tx to Connection struct
- Modify writer.rs to use tokio::select! for response + notification
- Add write_to_bytes() to OplockBreakNotification
- Support server→client async messages
Phase 5: WRITE Handler oplock break
- Get path/share_access before write
- Trigger OplockManager.break_oplock()
- Send OPLOCK_BREAK_NOTIFICATION to affected clients
- Encode and send via notification channel
All 229 tests pass.