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/server.rs

@@ -198,6 +198,8 @@ pub struct ServerState {
     pub shutting_down: Arc<AtomicBool>,
     /// Global oplock state manager (Phase 2).
     pub oplock_manager: Arc<crate::oplock::OplockManager>,
+    /// Global byte-range lock manager (Phase 7).
+    pub lock_manager: Arc<crate::oplock::LockManager>,
 }
 
 impl ServerState {
@@ -211,6 +213,7 @@ impl ServerState {
             shutdown: Arc::new(Notify::new()),
             shutting_down: Arc::new(AtomicBool::new(false)),
             oplock_manager: Arc::new(crate::oplock::OplockManager::new()),
+            lock_manager: Arc::new(crate::oplock::LockManager::new()),
         }
     }