use IIFE in app.html to prevent FOUC

src/app.html

@@ -8,6 +8,7 @@
 		<meta name="robots" content="noindex,nofollow" />
 		<script>
 			// On page load or when changing themes, best to add inline in `head` to avoid FOUC
+			(() => {
 				if (
 					localStorage.theme === 'light' ||
 					(!('theme' in localStorage) && window.matchMedia('(prefers-color-scheme: light)').matches)
@@ -36,6 +37,7 @@
 						}
 					}
 				});		
+			})();
 		</script>
 
 		%sveltekit.head%