Use native Codex runtime on Windows

[OldKrab]

Summary

• point codex-acp at the pinned native Windows codex.exe through CODEX_PATH
• validate that native runtime before publishing or reusing the managed installation
• remove the ineffective batch-launch detour from Fix managed Codex launch on Windows #338

Root cause

The Windows ACP process reaches @openaide/codex-acp, but its nested @openai/codex Node launcher exits during initialization. The package already carries a platform-native Codex executable. The same native executable was independently proven to complete an app-server initialize handshake on the Windows runner, and this failure mode is also documented by other ACP clients.

Local proof

• red/green provisioner test verifies Windows gets the exact managed native CODEX_PATH
• cargo test -p openaide-app-server codex_acp_provisioner
• cargo clippy -p openaide-app-server --all-targets -- -D warnings
• npm run check
• npm ci --os=win32 --cpu=x64 confirms the locked package contains the expected codex.exe