[KnightStackSys]

Summary

• Recognize native Chess.com FEN4 snapshots directly in match.openings_file, one per line, without requiring a fen prefix.
• Preserve existing fen ..., moves ..., SAN/PGN4, and optional | moves / | san entries.
• Tolerate UTF-8 BOMs from Windows text editors.
• Cover mixed opening books and paired games with a regression test.
• Document use with fixed matches, SPRT, and SPSA.

Testing

• Added a regression test in tests/test_san_openings.py.
• GitHub CI should run pytest on supported Python versions and OSes; full engine-play validation requires the IronPhoenix executable.