feat: polish app footer design and fix update time reactivity

[vantoan1511]

Summary

Polishes the application status bar (footer) to strictly adhere to Orbit's design principles and typography tokens, and makes the relative "last updated" time reactively update over time.

Changes

• AppFooter UI:
  • Added font-medium to the root footer status bar element.
  • Standardized inline icon-to-label gaps to gap-1.5.
  • Formatted all secondary status bar metadata in uppercase (.uppercase, K8S, AWS / EKS).
  • Added an interval timer (ticking every 10s) so the relative timestamp ("just now", "1m ago", etc.) updates dynamically as minutes pass.
• State Management:
  • Moved lastUpdatedAt into useKubernetesStore so that updates on initial data load and cluster switching are centralized and shared.
  • Updated useCluster composable to expose lastUpdatedAt as a reactive computed ref.

Files Changed

File	Change Type
src/components/layout/AppFooter.vue	Modified
src/composables/useCluster.ts	Modified
src/stores/kubernetesStore.ts	Modified

Testing

• Ran static type checking (vue-tsc --build) -> passed with 0 errors.
• Ran linting (eslint . --fix --max-warnings 0) -> passed with 0 errors.
• Ran production build (vite build) -> succeeded.

Related Issues

None