test(parser): normalize max-auth error prefix

[stacknil]

Summary

• normalize OpenSSH's leading error marker on maximum-authentication-attempts lines
• keep the variant in the existing max-auth / invalid-user event families
• add unit and fixture-matrix coverage plus parser contract wording

Validation

• cmake --build build --config Debug --target test_parser
• ctest --test-dir build -C Debug -R parser --output-on-failure
• cmake --build build --config Debug
• ctest --test-dir build -C Debug --output-on-failure
• git diff --check
• added-line privacy/secret scan