Add headless CLI, log rotation, configurable languages, and Windows subprocess fix

[quinnuk]

What's new

• Headless CLI mode (python main.py scan <folder> [options]) — run scans or continuous watching from the command line, no GUI/display required. Supports --dry-run, --watch, --languages, --keep-commentary, --subtitle-filter, --max-safety-mode, --persistent-backup, --quiet.
• Log rotation — audiocleaner_log.txt now rotates automatically at 5MB (keeping 2 backups), so a long-running Watch Mode instance no longer grows the log file without bound.
• Configurable preferred language(s) — audio language selection is no longer hardcoded to English; exposed via --languages in the CLI (e.g. --languages eng,jpn). Default behavior (English only) is unchanged.
• Fixed a real Windows bug — subprocess.run() calls for mkvmerge/mediainfo now explicitly pass stdin=subprocess.DEVNULL. Previously, an inherited-but-invalid stdin handle could raise OSError: [WinError 6] The handle is invalid on Windows in some launch contexts (e.g. a windowed/console-less process).
• Repo cleanup — stopped tracking the bundled MediaInfo CLI distribution (MediaInfo.exe, LIBCURL.DLL, Contrib/, Plugin/, etc.), PyInstaller build artifacts, and a stray compiled .pyc file. .gitignore updated accordingly, and build.bat now checks for the MediaInfo files first and gives a clear download link if they're missing, instead of failing inside PyInstaller.
• README updated with CLI usage docs and a new Repo Notes section.

Testing

16 new tests added (tests/test_cli.py, tests/test_logger_rotation.py). Full suite (82 tests) passes, including the real-mkvmerge integration tests in tests/test_integration_fixtures.py.