actually fix date input demo bad bind:value

src/routes/+page.svelte

@@ -57,7 +57,7 @@
 		{ value: 'option3', label: 'Option 3', disabled: true }
 	];
 	let lazyOptions: ComboboxOption[] = $state([]);
-	let dateInputValue = $state<CalendarDate | undefined>(undefined);
+	let dateInputValue = $state<CalendarDate | null>(null);
 	let checkboxValue = $state<CheckboxState>('indeterminate');
 	let dialogOpen = $state(false);
 	let scrollableDialogOpen = $state(false);