DOCFIX-165: Ceph replication tooling scripts, radosgw multisite + rbd-mirror (gap #5) ...

Extracts the Stage 6 runbook's manual command sequences into real,
parameterized scripts: scripts/dc-dc-radosgw-multisite.sh (master-init/
join-readonly/enable-two-way), scripts/dc-dc-rbd-mirror.sh
(bootstrap-primary/bootstrap-secondary --direction), scripts/dc-dc-dr-drill.sh
(failover/failback). The single most safety-critical property in the whole
drill -- demote the current primary before promoting the recovering side
during failback -- is hard-coded as fixed call order, not left to
documentation. Dry-run by default; --apply required for real execution,
plus a typed confirmation for the drill script. 19/19, 19/19, 23/23 tests.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QrcJx8TUar7pYAvpGJw57A