fix(gitlaunch): recover after protected push

[MCamner]

Summary

• avoid zsh's read-only status parameter in protected-push flows
• restore the base checkout on normal, EXIT, INT, and TERM paths
• keep signal-safe Gitlaunch exits inside the Git menu
• add an executable regression test against the real Gitlaunch implementation

Verification

• tests/mq-git-protected-push-smoke.sh
• tests/gitlaunch-pr-push-recovery-smoke.sh
• tests/gitlaunch-menu-surface-smoke.sh
• tests/git-restore-to-base-smoke.sh
• tests/test-inventory-smoke.sh
• shell syntax checks and git diff --check