feat: add ECR image and stale tag browser

[YoungJinJung]

Summary

Add an ECR image and tag browser so users can inspect what image versions exist in a repository and identify stale images.

Scope

• Show tags, digests, pushed time, and image size for a selected repository
• Highlight untagged images and older candidates for cleanup
• Provide clipboard-friendly digest/tag values for follow-up use

Acceptance Criteria

• Selecting an ECR repository opens an image/tag list
• The image list includes digest, pushed time, and size metadata
• The view clearly surfaces untagged or stale images
• Tests cover image metadata mapping and the navigation flow
• README is updated

[YoungJinJung]

@Unic-bot: assign me

[github-actions]

@YoungJinJung has been assigned to this issue.

[YoungJinJung]

Implemented on main via the ECR repository/image browser work. The current main branch includes repository-to-image navigation, image tag/digest/pushed-time/size metadata, untagged and stale cleanup signals, clipboard-friendly image detail values, tests for mapping/navigation, and README updates.