- 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.