Document actual groups.promote/groups.demote parameters and required
old-writer fencing before confirmation. Demotion is a controlled rejoin
step, not an atomic promote-then-demote handover or log reconciliation.
Clarify replica coverage, confirmation meaning, and lineage readback.
Corrected redo of #104342; its nonexistent groups.peer methods and unsafe
handover ordering are not carried forward.
Fixes#104309
Refs #104904
Co-authored-by: Rohith Pariki <rohithpariki@gmail.com>