docs(release-notes): flag user-visible behavior changes as drafting input

V1.39.x shipped two intentional behavior changes whose commit subjects
read as fixes: 37a446c9 narrowed VPN detection (split-tunnel VPN users
no longer trigger Network Stack Refresh) and 357ee057 removed the
Bluetooth reset task. The commit bodies are clear, but the release-notes
skill's "Inputs to gather" list only asked the drafter to look at
oneline subjects, so the kind of items that need notes but do not
look like bug fixes are easy to miss.

Add scanning full commit message bodies for "controlled regression"
and similar wording as an explicit drafting step, with both commits
as worked examples.