brdev: Add cluster management commands

[ytsssun]

Summary

The forest needs centralized cluster management in brdev to simplify launching Bottlerocket instances. Currently, the launch-bottlerocket-ec2 skill requires manual lookup of cluster details (endpoint, CA, etc.).

Proposed Features

brdev cluster list              # List known clusters (EKS/ECS)
brdev cluster create <name>     # Create a test cluster
brdev cluster status <name>     # Show cluster details
brdev cluster delete <name>     # Clean up cluster

Benefits:

• Abstracts away cluster CA/endpoint lookup
• Tracks clusters created for testing
• Enables easy cleanup of test resources
• Skills can reference clusters by name instead of raw IDs

Context

From PR #2 review comment by @cbgbt:

"This is fine for now, but we probably want some forest-wide sense of cluster management. In other words, there should be a brdev tool for cluster management and an easy way to see which clusters exist and their status (abstracted away in brdev). Then rather than needing to get the CAs, the tooling can manage it."