ReleaseProcessOverview.md: enshrine "don't ship on a Friday/before a
holiday" in Step 1, and add explicit preview-first guidance for
merge/copy operations.
Per discussion in today's Escalations meeting, Technical Support
asked that the "don't release on a Friday (or just before a major
holiday)" practice be made explicit in the release process itself,
not just informally followed. Added as a callout at the top of
Step 1 (Plan!).
Also added a general "always preview before merging or copying"
best practice alongside the existing "Merge Down, Copy Up" mantra:
run the '-n' preview first, then either start with nothing already
opened, confirm nothing already opened conflicts with what the
preview shows, or knowingly proceed with opened files if that's
actually intended -- an opened file caught up in a merge isn't
something to avoid at all costs, just something to not be
surprised by. Updated Step 10 (Copy Up) to show the '-n' preview
explicitly, matching Step 9 (Merge Down)'s existing pattern.