Machine number input at PXE menu for Standard PCs

Adds a machine number prompt to startnet.cmd after the Standard sub-type
selection. Tech enters the number during the PXE boot process. Defaults
to 9999 if Enter is pressed (existing placeholder behavior).

Written to C:\Enrollment\machine-number.txt alongside pc-type.txt.

Consumers:
  00-PreInstall-MachineApps.ps1 - replaces 9999 in UDC InstallArgs with
    the entered number, so UDC installs with the correct machine number
    from the start (no post-setup Set-MachineNumber needed).
  01-eDNC.ps1 - writes the machine number to the DNC\General\MachineNo
    registry value during eDNC install.
  Configure-PC.ps1 - existing $needsMachineNumber check already skips
    the prompt when UDC/eDNC aren't at 9999, so no change needed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

playbook/startnet.cmd

@@ -122,6 +122,13 @@ set /p standard_choice=Enter your choice (1-2):
 if "%standard_choice%"=="1" set PCSUBTYPE=Timeclock
 if "%standard_choice%"=="2" set PCSUBTYPE=Machine
 if "%PCSUBTYPE%"=="" goto standard_menu
+
+REM --- Machine number (Standard only) ---
+set MACHINENUM=9999
+echo.
+set /p MACHINENUM=Enter machine number (digits, or Enter for 9999):
+if "%MACHINENUM%"=="" set MACHINENUM=9999
+echo Machine number: %MACHINENUM%
 :skip_standard_menu
 
 REM --- Display sub-type ---
@@ -278,6 +285,7 @@ if "%PCTYPE%"=="" goto cleanup_enroll
 echo %PCTYPE%> W:\Enrollment\pc-type.txt
 if not "%DISPLAYTYPE%"=="" echo %DISPLAYTYPE%> W:\Enrollment\display-type.txt
 if not "%PCSUBTYPE%"=="" echo %PCSUBTYPE%> W:\Enrollment\pc-subtype.txt
+if not "%MACHINENUM%"=="" echo %MACHINENUM%> W:\Enrollment\machine-number.txt
 copy /Y "Y:\shopfloor-setup\Run-ShopfloorSetup.ps1" "W:\Enrollment\Run-ShopfloorSetup.ps1"
 REM --- Always copy Shopfloor baseline scripts ---
 mkdir W:\Enrollment\shopfloor-setup 2>NUL