Implement SMB Oplocks Phase 3+5

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.

vendor/smb-server/src/proto/messages/oplock_break.rs

@@ -33,6 +33,12 @@ impl OplockBreakNotification {
         out.extend_from_slice(&c.into_inner());
         Ok(())
     }
+    /// Phase 3: Write to a new Vec (convenience method).
+    pub fn write_to_bytes(&self) -> Vec<u8> {
+        let mut buf = Vec::new();
+        self.write_to(&mut buf).expect("encode notification");
+        buf
+    }
 }
 
 /// SMB2_OPLOCK_BREAK_ACK (MS-SMB2 §2.2.24.1) — same wire shape as the