SDP_DeveloperGuide.adoc / ReleaseProcessOverview.md: make explicit that Copy Up is reserved for coordinated release activity (Release Process Step 10, EBF Merge Down, or a doc-only Hot Fix in main), not something to do ad hoc for an individual dev fix.
Merge Down remains fine to do routinely.
Prompted by the user's correction after today's SDP-1397 work: main is meant to reflect the most recently shipped release, not a preview of upcoming dev work. Deliberately staying in dev only for now, per the policy this documents.