Addresses code review:
- Important #4: finish now fetches issue title via `gh issue view --json title`
and uses it as PR title (was using the branch name). Falls back to branch
name if the fetch fails or returns empty.
- Minor #8: explicit `return 4` on `git push` failure for consistency with
the documented exit-code contract.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Also patches gh-mock to sanitize dashes in branch-derived env var names,
and fixes --head two-arg parsing in the pr view mock handler.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
