Linux/Python 3.14: heredoc-based python snippets can fail with multiprocessing <stdin> FileNotFoundError

## Summary
On Ubuntu 26.04 + Python 3.14, running validation/demo snippets via heredoc (`python - <<'PY' ...`) can produce:

`FileNotFoundError: ... `

from `multiprocessing/forkserver` / `spawn`.

This appears as an installation/runtime failure, even when device setup is actually correct.

## Environment
- Ubuntu 26.04.1 LTS
- Python 3.14.4
- OpenVINO 2026.3.1

## Repro pattern
Any script/snippet that executes Python from stdin and triggers multiprocessing/spawn path can fail with missing `` pseudo-file.

## Expected
Validation snippets should run reliably on Python 3.14 without false-negative errors.

## Actual
Traceback points to `` and suggests failure while stack/device setup may still be functional.

## Workaround we used (successful)
Instead of heredoc, write code to a real file and run it:
1. `cat > test.py <<'PY' ... PY`
2. `python test.py`

After switching to file-based execution, checks ran cleanly and NPU detection/inference worked.

## Suggested fix
Update docs/scripts to avoid stdin-executed Python for validation tasks on Linux (especially Python 3.14+).

Search the repository for validation or demo snippets that invoke Python via heredoc, then read the surrounding documentation or scripts. Reproduce the Linux/Python 3.14 path and update the affected instructions or script to use a file-based invocation; done means validation completes without the multiprocessing error.

Written by the indexing model from the issue text.