feat: show EC2 related resources for instances

[nathanhuh]

Problem

After selecting an EC2 instance, users should be able to move through the AWS resources that explain how that instance is connected to traffic and scaling paths.

Scope

Build on the EC2 Instance Browser and add relationship navigation from instance detail to:

• Security groups attached to the instance
• Auto Scaling Group membership, when present
• Target groups where the instance is registered
• Load balancers associated with those target groups
• Listeners and listener rules for those load balancers

UX Notes

• Use drill-down list/detail screens instead of a dense all-in-one detail page.
• Related resource lists should use the same filter, wrap navigation, refresh, and empty-state patterns as other unic lists.
• Make it clear when a relationship is unavailable because the instance has no association versus because an API call failed or permissions are missing.

AWS Notes

• ASG can be inferred from Auto Scaling APIs and/or the aws:autoscaling:groupName tag where available.
• Target groups can be resolved through ELBv2 target health registration.
• Load balancers and listeners should be resolved through ELBv2 APIs from target group/load balancer ARNs.

Acceptance Criteria

• From an EC2 instance detail screen, users can open related security groups, ASG, target groups, load balancers, and listeners where available.
• Each related list is filterable and navigable with wrap behavior.
• Empty relationships render a useful empty state.
• Permission/API failures do not crash the TUI and produce actionable errors or partial results.
• Tests cover relationship mapping and TUI navigation for at least the main relationship paths.
• README documents the related-resource browser behavior.

Dependency

• Depends on the EC2 Instance Browser base issue.

[nathanhuh]

@Unic-bot: assign me

[github-actions]

@nathanhuh has been assigned to this issue.