feat: Add IAM access key rotation support (M3.3)

[nathanhuh]

Summary

Add support for listing and rotating IAM access keys in the TUI. This complements #14 (IAM ListUsers) by providing credential lifecycle management.

Details

• List access keys for the current user or a selected user, showing key ID, status, age, and last used date
• Rotate keys: create new key → display credentials once → deactivate old key (with confirmation)
• Visual warning for aged keys (e.g., >90 days)
• Copy new credentials to clipboard

Checklist

• Add ListAccessKeys and RotateAccessKey feature kinds in internal/domain/model.go
• Register features in internal/domain/catalog.go under IAM service
• Implement ListAccessKeys() in internal/services/aws/iam.go
• Implement RotateAccessKey() with create → display → deactivate flow
• Add key age calculation and status display
• Add confirmation screen before key rotation
• Add screen transitions in internal/app/
• Write tests

[YoungJinJung]

@Unic-bot: assign me

[github-actions]

@YoungJinJung has been assigned to this issue.