Implement SMB Byte-range Lock (Phase 7)

- Add LockManager to oplock.rs:
  - LockRange struct for tracking byte-range locks
  - acquire() - check conflicts before granting lock
  - release() - remove specific lock by offset/length
  - clear() - clear all locks when file closed
  - ranges_overlap() - helper for conflict detection

- Add LockManager to ServerState

- Update handlers/lock.rs:
  - Parse LockRequest and LockElement
  - Process each lock element (acquire/release)
  - Support FLAG_EXCLUSIVE_LOCK, FLAG_SHARED_LOCK, FLAG_UNLOCK
  - Return STATUS_LOCK_NOT_GRANTED on conflict

- Update handlers/close.rs:
  - Clear all locks when file closed

- Add STATUS_LOCK_NOT_GRANTED to ntstatus.rs

All 229 tests pass.

vendor/smb-server/src/handlers/close.rs

@@ -52,6 +52,9 @@ pub async fn handle(
         server.oplock_manager.unregister(&path, &req.file_id).await;
     }
 
+    // Phase 7: Clear all byte-range locks for this file
+    server.lock_manager.clear(&req.file_id).await;
+
     // Stat before closing if needed.
     let info_before_close = if want_attrs {
         if let Some(h) = handle.as_ref() {