fix: clean up all event listeners in +layout.svelte onMount (open-webui#20913)

Extract anonymous touch event handlers into named functions and add
proper cleanup for all event listeners (message, touchstart, touchmove,
touchend, visibilitychange) in the onMount return function.

Previously only the resize listener was being cleaned up, causing
memory leaks during navigation and hot-reloads.

Author: sjhddh

src/routes/+layout.svelte

@@ -629,28 +629,32 @@
 			return nav && (el === nav || nav.contains(el));
 		}
 
-		document.addEventListener('touchstart', (e) => {
+		const touchstartHandler = (e) => {
 			if (!isNavOrDescendant(e.target)) return;
 			touchstartY = e.touches[0].clientY;
-		});
+		};
 
-		document.addEventListener('touchmove', (e) => {
+		const touchmoveHandler = (e) => {
 			if (!isNavOrDescendant(e.target)) return;
 			const touchY = e.touches[0].clientY;
 			const touchDiff = touchY - touchstartY;
 			if (touchDiff > 50 && window.scrollY === 0) {
 				showRefresh = true;
 				e.preventDefault();
 			}
-		});
+		};
 
-		document.addEventListener('touchend', (e) => {
+		const touchendHandler = (e) => {
 			if (!isNavOrDescendant(e.target)) return;
 			if (showRefresh) {
 				showRefresh = false;
 				location.reload();
 			}
-		});
+		};
+
+		document.addEventListener('touchstart', touchstartHandler);
+		document.addEventListener('touchmove', touchmoveHandler, { passive: false });
+		document.addEventListener('touchend', touchendHandler);
 
 		if (typeof window !== 'undefined') {
 			if (window.applyTheme) {
@@ -842,11 +846,15 @@
 
 		return () => {
 			window.removeEventListener('resize', onResize);
+			window.removeEventListener('message', windowMessageEventHandler);
+			document.removeEventListener('touchstart', touchstartHandler);
+			document.removeEventListener('touchmove', touchmoveHandler);
+			document.removeEventListener('touchend', touchendHandler);
+			document.removeEventListener('visibilitychange', handleVisibilityChange);
 		};
 	});
 
 	onDestroy(() => {
-		window.removeEventListener('message', windowMessageEventHandler);
 		bc.close();
 	});
 </script>