Add cluster slot heatmap visualization #470

Description

Add a visual heatmap to the cluster view that shows slot-level CPU utilization across the cluster using CLUSTER SLOT-STATS. This helps operators quickly identify hot slots and unbalanced load distribution for resharding decisions.

Prior Art

The slot-level approach for identifying hot keys via CLUSTER SLOT-STATS was already implemented in PR #105. This issue extends that work into a visual heatmap representation that surfaces hot slots at a glance without requiring the user to start MONITOR.

Requirements

• Visual heatmap of slot ranges colored by CPU microseconds
• Requires cluster-slot-stats-enabled to be set on the cluster
• Drill-down from hot slot to the keys within that slot

Target Release

1.3.0 (September)