feat: improve mobile touch behavior on Snellen chart

- Capture touch coordinates and apply radial gradient mask at touch point
- Single touch now shows unblurred area exactly where user touched (matching mouse behavior)
- Unblurs for 6 seconds then re-blurs automatically

Author: vinutv

src/components/error-pages/load-failed.tsx

@@ -95,20 +95,30 @@ export default function LoadFailedErrorPage() {
     }
   }, []);
 
-  // Touch handler for mobile (trigger brief unblur)
-  const handleTouchStart = useCallback(() => {
+  // Touch handler for mobile (trigger unblur with touch position)
+  const handleTouchStart = useCallback((e: TouchEvent) => {
     if (touchTimeoutRef.current) {
       clearTimeout(touchTimeoutRef.current);
     }
 
+    // Get touch coordinates relative to container
+    const touch = e.touches[0];
+    const rect = containerRef.current?.getBoundingClientRect();
+    if (rect && touch) {
+      setMousePos({
+        x: touch.clientX - rect.left,
+        y: touch.clientY - rect.top,
+      });
+    }
+
     setIsUnblurred(true);
     touchTimeoutRef.current = setTimeout(() => {
       setIsUnblurred(false);
       touchTimeoutRef.current = null;
     }, TOUCH_UNBLUR_DURATION);
   }, []);
 
-  // Clean up touch on touchend to allow state reset
+  // Clean up touch on touchend
   const handleTouchEnd = useCallback(() => {
     // Timeout continues to manage the blur
   }, []);