fix: guard question log payload args

[hiSandog]

Summary

• Add an explicit argument count check to gstack-question-log before reading $1 under set -u
• Return a clear usage error when the JSON payload argument is missing
• Add regression coverage for the missing-payload path

Tests

• env PATH=/Users/sandog/.real/.bin:/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin /Users/sandog/.real/.bin/bun test test/gstack-question-log.test.ts
• git diff --check