Refactor IAM dashboard widgets

[roncodes]

Summary

• replaces the legacy IAM home metrics card with the Dashboard-powered IAM widget suite
• registers dedicated IAM KPI, security, governance, activity, and quick-action widgets
• adds IAM dashboard styling and widget registration coverage

Verification

• eslint addon/extension.js tests/unit/extension-test.js --cache-location /tmp/iam-engine-eslintcache
• ember-template-lint addon/components/widget/recent-activity.hbs addon/components/widget/quick-actions.hbs