Fix OpenCode plugin template to keep subprocess output out of the TUI

@elprans is attempting to deploy a commit to the Yury Selivanov's projects Team on Vercel.

A member of the Team first needs to authorize it.

Thanks for testing with OpenCode and the fixes. Replacing execSync by spawnSync is a great improvement.

JSON.stringify() is prone to injections. Maybe remove quote() altogether and expand the command() interface. Safer and simpler.

Suggested changes: opencode-plugin.ts