Replaces hardcoded `gh pr create` in Option 2 with a platform-neutral
note: check `git remote get-url origin` first, then use gh (GitHub),
glab (GitLab), or fall back to the compare URL for unknown platforms.
Adds matching Red Flag entry so agents don't skip the detection step.
Fixes#1609
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
