feat: replace all vanilla HTML elements with shadcn components

- Install skeleton and tooltip shadcn components
- event-dialog: textarea → Textarea, duration chips → Button ghost
- date-time-picker: raw button trigger → Button outline, quick-date chips → Button ghost
- event-card: <a> URL link → Button link asChild
- sign-in: animate-pulse div → Skeleton
- ai-toolbar: animate-pulse div → Skeleton, event count span → Badge secondary
- event-actions-toolbar: event count span → Badge secondary

src/components/event-card.tsx

@@ -95,16 +95,22 @@ export const EventCard = ({ event, onEdit, onDelete }: EventCardProps) => {
 							)}
 
 							{event.url && (
-								<a
-									href={event.url}
-									target="_blank"
-									rel="noopener noreferrer"
-									className="inline-flex items-center gap-1 text-primary/70 hover:text-primary transition-colors"
-									onClick={(e) => e.stopPropagation()}
+								<Button
+									variant="link"
+									size="sm"
+									className="inline-flex items-center gap-1 h-auto p-0 text-xs text-primary/70 hover:text-primary"
+									asChild
 								>
-									<ExternalLink className="h-3 w-3" />
-									<span className="truncate max-w-[120px]">Link</span>
-								</a>
+									<a
+										href={event.url}
+										target="_blank"
+										rel="noopener noreferrer"
+										onClick={(e) => e.stopPropagation()}
+									>
+										<ExternalLink className="h-3 w-3" />
+										<span className="truncate max-w-[120px]">Link</span>
+									</a>
+								</Button>
 							)}
 						</div>