adapt mainboard board id writer script for Windows

The original error was:

can't open file '...\venv\Scripts\python.exe': [Errno 2] No such file or directory

Cause: On Windows, your script tried to restart itself inside the venv using:

os.execv(venv_python, [str(venv_python)] + sys.argv)

• Windows interpreted the target venv Python path incorrectly, duplicating the path
  (e.g., \.venv\review\rebuild\fw-main…\.venv\Scripts\python.exe)
• This happens because python3 points to the Windows Store Python launcher, which doesn’t handle execv correctly.

Summary: The script’s automatic venv re-exec using os.execv() was not compatible with Windows, causing a “file not found” error.

The fix: use absolute paths and on Windows restart via subprocess.run() instead of os.execv().

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after that it works