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/sign-in.tsx

@@ -4,6 +4,7 @@ import { LogIn, LogOut } from "lucide-react";
 import { useRouter } from "next/navigation";
 import { toast } from "sonner";
 import { Button } from "@/components/ui/button";
+import { Skeleton } from "@/components/ui/skeleton";
 import { signOut, useSession } from "@/lib/auth-client";
 
 export default function SignIn() {
@@ -20,7 +21,7 @@ export default function SignIn() {
 	};
 
 	if (isPending) {
-		return <div className="h-8 w-16 bg-muted animate-pulse rounded-md" />;
+		return <Skeleton className="h-8 w-16" />;
 	}
 
 	if (session?.user) {