Fix managed Codex launch on Windows

[OldKrab]

Summary

• launch the pinned managed Codex ACP package through npm's generated Windows batch shim
• validate the platform launcher before publishing or reusing a managed runtime
• preserve the direct Node launch on non-Windows platforms

Root cause

The managed runtime changed Windows from the previously working batch-mediated process launch to direct node.exe stdio. The packaged ACP smoke then lost the agent during initialize even though Codex itself started successfully. This restores cmd.exe mediation without returning to npx or network-at-launch behavior.

Verification

• cargo test -p openaide-app-server codex_acp_provisioner
• cargo clippy -p openaide-app-server --all-targets -- -D warnings
• npm run check