feat: added new components

[chriz-cloud]

Summary

• Add LoadingSpinner with inline and full-page variants (3 sizes)
• Add PageSkeleton shimmer placeholder matching dashboard card dimensions
• Add ErrorState with title, message, and optional onRetry callback
• Add EmptyState with swappable icon, description, and CTA slot
• Wire all four states into dashboard/page.tsx behind ?ui= query flags for preview

Components

Component	Path
LoadingSpinner	src/components/ui/loading-spinner.tsx
PageSkeleton	src/components/ui/page-skeleton.tsx
ErrorState	src/components/ui/error-state.tsx
EmptyState	src/components/ui/empty-state.tsx

How to preview

Start the dev server and navigate to /dashboard with one of the following query params:

Param	State shown
?ui=loading	PageSkeleton
?ui=loading-page	LoadingSpinner full-page overlay
?ui=error	ErrorState
?ui=empty	EmptyState with CTA button
(none)	Normal dashboard

Notes

• All components accept className for layout flexibility
• ErrorState.onRetry is optional — the retry button only renders when provided
• Components are server-renderable (no client-only hooks)
• Follows existing CVA + cn() + lucide-react conventions

closes #10

[aji70]

@chriz-cloud resolve conflicts