fix: Replace NUL device references with DOS 6.22 compatible tests

Critical fix for DOS 6.22 compatibility - NUL is a reserved device name
in both DOS and Windows and cannot be used as a file/directory name.

Problem:
- "T: 2>NUL" attempts to create a file called "NUL" (not allowed)
- "IF NOT EXIST T:\NUL" tests for NUL device (unreliable)
- "IF NOT EXIST path\NUL" treats NUL as filename (invalid)

Solution - Replaced with proper DOS 6.22 tests:
- "T: 2>NUL" → "DIR T:\ >nul" (test drive access via directory listing)
- "IF NOT EXIST T:\NUL" → "IF NOT EXIST T:\*.*" (test for any files)
- "IF NOT EXIST path\NUL" → "IF NOT EXIST path\*.*" (test directory)

Note: Using lowercase "nul" for output redirection is acceptable as
it redirects to the NUL device, but NUL as a filename/path is invalid.

Files updated:
- DEPLOY.BAT: Fixed drive and directory tests
- UPDATE.BAT: Fixed drive and directory tests
- NWTOC.BAT: Fixed drive and directory tests
- CTONW.BAT: Fixed drive and directory tests
- CHECKUPD.BAT: Fixed drive and directory tests
- DOSTEST.BAT: Fixed drive and directory tests

Created fix-nul-references.ps1:
- Automated script to find and fix NUL references
- Preserves CRLF line endings
- Updates all BAT files consistently

Created monitoring scripts:
- monitor-sync-status.ps1: Periodic sync monitoring
- quick-sync-check.ps1: Quick AD2-to-NAS sync status check

Verification:
- All BAT files maintain CRLF line terminators
- File sizes increased slightly (4-8 bytes) due to pattern changes
- DOS 6.22 compatible wildcard tests (*.*) used throughout

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

DEPLOY.BAT

@@ -39,11 +39,11 @@ REM ==================================================================
 ECHO [STEP 1/5] Checking network drive...
 ECHO.
 
-T: 2>NUL
+DIR T:\ >nul
 IF ERRORLEVEL 1 GOTO NO_T_DRIVE
 
 C:
-IF NOT EXIST T:\NUL GOTO NO_T_DRIVE
+IF NOT EXIST T:\*.* GOTO NO_T_DRIVE
 
 ECHO [OK] T: drive is accessible
 ECHO     T: = \\D2TESTNAS\test
@@ -172,8 +172,8 @@ IF EXIST C:\AUTOEXEC.BAT (
 ECHO.
 
 REM Create C:\BAT directory if it doesn't exist
-IF NOT EXIST C:\BAT\NUL MD C:\BAT
-IF NOT EXIST C:\BAT\NUL GOTO BAT_DIR_ERROR
+IF NOT EXIST C:\BAT\*.* MD C:\BAT
+IF NOT EXIST C:\BAT\*.* GOTO BAT_DIR_ERROR
 
 ECHO Copying update system files to C:\BAT\...