fix(mxc): add schema version to test configs (NVBug 6842812)

[prekshivyas]

Summary

Fix the shipped Windows MXC OCSF-audit and WebSocket gateway configurations so the current gateway accepts them. Both examples omitted the mandatory gateway schema header and failed before the MXC driver could start.

Related Issue

• NVBug 6842812
• No public GitHub issue required: localized Windows MXC example configuration bug.

Before / after reproduction

Before this change, each command exited 1 with gateway config schema version is required; add [openshell] and version = 2:

• openshell-gateway.exe --config crates\openshell-driver-mxc\examples\mxc-ocsf-audit.toml
• openshell-gateway.exe --config crates\openshell-driver-mxc\examples\mxc-ws-gateway.toml

After this change, the identical commands pass schema validation. With the runners' OPENSHELL_DRIVERS=mxc environment, both configurations reach normal gateway startup/listening.

Changes

• Add [openshell] with version = 2 to both shipped configurations.
• Add a typed TOML regression test that requires the current schema in both files.

Testing

• mise run pre-commit passes
  • Attempted on Windows ARM64; the unrelated Biome executable crashes with 0xC0000005.
• Unit tests added/updated
  • cargo test -p openshell-driver-mxc --test demo_examples -- --nocapture: 6 passed after rebasing onto the current windows tip.
• E2E tests added/updated (not applicable)
• Exact gateway before/after reproduction completed.
• cargo fmt --all -- --check
• git diff --check

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (not applicable)

[shailendra-nv]

Reviewed the full diff at 335930f against the current windows base. No blocking findings. Both example headers match gateway schema version 2; the regression test covers missing, incorrectly typed, and incorrect versions. Independent before/after TOML checks passed for both files with all other settings unchanged. Branch checks passed. Windows CI and E2E jobs were skipped; native Windows and real-MXC execution were not independently rerun during review.