combobox: don't highlight first item on first open

src/lib/Combobox.svelte

@@ -114,6 +114,7 @@
 
 	/** stores currently highlighted option (according to keyboard navigation or default item) */
 	let highlighted = $derived.by((): ComboboxOption | undefined => {
+		if (!searching) return undefined; // otherwise, the first item is highlighted on first open
 		if (filteredItems.length === 0) return undefined;
 		if (value !== undefined && filteredItems.find((v) => v.value === value?.value)) return value;
 		if (!filteredItems[0]?.disabled) return filteredItems[0];