Convert dashboard from nested row panels to flattened sibling panels.
Grafana v10 requires all panels to be at the root level; rows are
just visual separators with collapsed state.
Closes: miroir-afh.3
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Add collapsed Resharding (§13.1) feature-gated row with phase gauge,
in-progress stat, and backfill rate panel. Fix overlapping y=74 on
Anti-Entropy and Settings Broadcast rows by shifting subsequent rows.
Sync charts/miroir/dashboards/ copy with root dashboard.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>