fix(ci): restore Windows test portability

[pimlock]

Summary

Restore portability of two tests that broke the advisory Windows MSVC checks on main, and make Unix-specific pre-commit tasks behave correctly under native Windows.

The regressions were introduced by:

• feat(mxc): add Windows ETW-to-OCSF audit trail #3015 changed OCSF device identity to use the current host OS but left an integration test expecting Linux unconditionally.
• refactor(config): normalize and enforce gateway schema v2 #2814 inserted a new test between #[cfg(unix)] and the FIFO test, leaving the nix-dependent FIFO test enabled on Windows.

Related Issue

No issue required: this is an obvious localized correction to two test regressions and their native-Windows validation path.

Changes

• Expect the OCSF device OS name to match the build platform.
• Restore the Unix-only guard on the FIFO test that uses nix::unistd::mkfifo.
• Explicitly skip the Unix shell-based Cargo lockfile check on native Windows.
• Use npm's Windows buf.cmd shim for proto:lint.

Testing

• mise run pre-commit completes on native Windows
• mise run windows:test:x64 (3,540 passed, 16 skipped)
• Native Windows Rust lint, including the e2e and example manifests
• E2E tests added/updated (not applicable; test and task portability fixes)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

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[pimlock]

/ok to test b775f59

[pimlock]

/ok to test fc74d79