refactor(actions): extract clickOutside to shared module, replace 5 inline copies

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/UserMenu.svelte

@@ -1,27 +1,17 @@
 <script lang="ts">
 import { enhance } from '$app/forms';
 import { m } from '$lib/paraglide/messages.js';
+import { clickOutside } from '$lib/actions/clickOutside';
 
 let { userInitials }: { userInitials: string | null } = $props();
 
 let userMenuOpen = $state(false);
-
-function clickOutside(node: HTMLElement) {
-	const handleClick = (event: MouseEvent) => {
-		if (node && !node.contains(event.target as Node) && !event.defaultPrevented) {
-			userMenuOpen = false;
-		}
-	};
-	document.addEventListener('click', handleClick, true);
-	return () => {
-		document.removeEventListener('click', handleClick, true);
-	};
-}
 </script>
 
 <div
 	class="relative"
-	{@attach clickOutside}
+	use:clickOutside
+	onclickoutside={() => (userMenuOpen = false)}
 	onkeydown={(e) => {
 		if (e.key === 'Escape') userMenuOpen = false;
 	}}