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/ntstatus.rs

@@ -39,3 +39,4 @@ pub const STATUS_INFO_LENGTH_MISMATCH: u32 = 0xC000_0004;
 pub const STATUS_FILE_CLOSED: u32 = 0xC000_0128;
 pub const STATUS_INVALID_INFO_CLASS: u32 = 0xC000_0003;
 pub const STATUS_NO_EAS_ON_FILE: u32 = 0xC000_0052;
+pub const STATUS_LOCK_NOT_GRANTED: u32 = 0xC000_0054; // Phase 7: byte-range lock conflict