integration: real git push through a chained pre-push with OPF failing

Installs a user pre-push hook, then Entire's hooks through the real CLI so the user hook is chained, configures a local OPF command that fails closed, and runs a real git push to a bare remote. The push must be rejected and the user hook skipped; a positive control checks the chained hook still runs when Entire's pre-push succeeds. Fails without the status guard.