feat(frontend): better stealth overlay

frontend/src/lib/components/StealthOverlay.svelte

@@ -1,7 +1,16 @@
 <script lang="ts">
+	import { onMount } from 'svelte';
+
 	let stealthMode = $state(false);
 	let lastTap = $state({ time: 0, x: 0, y: 0 });
 
+	onMount(() => {
+		document.body.style.touchAction = 'manipulation';
+		return () => {
+			document.body.style.touchAction = '';
+		};
+	});
+
 	function isInCenterZone(x: number, y: number): boolean {
 		const w = window.innerWidth;
 		const h = window.innerHeight;
@@ -25,7 +34,7 @@
 		const distX = Math.abs(x - lastTap.x);
 		const distY = Math.abs(y - lastTap.y);
 
-		if (timeDiff < 300 && distX < 50 && distY < 50) {
+		if (timeDiff < 500 && distX < 50 && distY < 50) {
 			stealthMode = !stealthMode;
 			lastTap = { time: 0, x: 0, y: 0 };
 			e.preventDefault();