Manual QA checklist from a diff

Produce a short checklist a human can click through in the deployed app to confirm this change works. The reader is a person with a browser and a test account — not a developer reading code. Every step must be something they can do and observe through the UI (or, rarely, an email inbox / API client if the change only surfaces there).

This is not a regression suite and not a code review. Cover only what this diff changed, plus the one or two adjacent flows most likely to break as a side effect. If the checklist grows past ~10 steps, it's too broad — cut it back to what the change actually touched.

1. Get the diff

Default to comparing the current branch against main; respect any base, commit range, or PR the user names instead.